Indispensable Co-litigation in Japan (Koyū Hitsuyōteki Kyōdō Soshō) - Part 2: How are Non-Cooperative Co-Plaintiffs Handled and What is the True Meaning of "Uniformity of Judgment"?

Japanese Attorney at Law - Bengoshi L.L.

01 Jun 2025 • 9 min read

In Part 1 of this series, we established that Indispensable Necessary Co-litigation (Koyū Hitsuyōteki Kyōdō Soshō - 固有必要的共同訴訟) in Japan mandates the joinder of all essential parties for a lawsuit to proceed validly and for its judgment to achieve "Uniformity of Judgment" (gōitsu kakutei - 合一確定) concerning all such parties. This necessity often stems from the nature of the underlying substantive right, particularly when it requires joint management or disposition by multiple individuals. However, a significant practical challenge arises: what happens if one or more of these essential parties, especially those who would typically be co-plaintiffs, refuse to cooperate in bringing the lawsuit? Can the willing parties still pursue their claim, or is their access to justice effectively blocked? This article delves into the evolving Japanese case law on handling these "non-cooperative potential co-plaintiffs" (teiso hi-dōchōsha - 提訴非同調者) and how this impacts the understanding of "joint litigation" and "uniformity of judgment."

The Traditional Dilemma: Non-Cooperation and the Risk of Denied Access to Justice

The traditional understanding of indispensable necessary co-litigation, particularly where the requirement for joint action arises from substantive law (e.g., rights that can only be exercised collectively), posed a significant hurdle if some potential co-plaintiffs were unwilling to participate. If all right-holders were required to sue jointly as plaintiffs for the court to recognize proper party standing, the refusal of even one such individual to join could lead to the dismissal of the action. This effectively gave a single non-cooperative party a veto over the ability of other willing parties to seek judicial redress, potentially denying them their fundamental right to sue (soken no hogo - 訴権の保護, protection of the right to sue).

The reasons for non-cooperation can be diverse:

Genuine disagreement with the merits or timing of the lawsuit.
A desire to align with the opposing party.
A general aversion to litigation (famously encapsulated in a line from Kenji Miyazawa's poem "Ame ni mo Makezu," suggesting one should tell people to stop pointless quarrels and lawsuits).
Strategic considerations, such as believing the other potential plaintiffs are rushing into litigation unprepared.

While forcing all potential co-plaintiffs to join as defendants might seem like a straightforward solution, this approach was long considered a "forbidden move" (kinjite - 禁じ手) by the Japanese Supreme Court, primarily due to concerns about distorting the true adversarial structure and the distinct roles of plaintiffs and defendants.

An Early, Specialized Solution: Boundary Determination Suits

An initial, albeit context-specific, departure from this rigidity came in a Supreme Court decision concerning a boundary determination suit (kyōkai kakutei soshō - 境界確定訴訟) involving co-owned land (Supreme Court, November 9, 1999, Minshu Vol. 53, No. 8, p. 1421).

In this type of action, which is considered a "formal formative action" (keishiki-teki keisei soshō - 形式的形成訴訟) where the court actively demarcates a boundary rather than merely declaring pre-existing rights, the Supreme Court permitted non-cooperative co-owners (who would logically be co-plaintiffs alongside other co-owners of their parcel) to be named as defendants. This was allowed alongside the owners of the adjacent land (the primary defendants).

The rationale, as particularly elucidated in Justice Chigusa's supplementary opinion to the 1999 judgment, was that this was a "measure of convenience" (benpō - 便法) justified by the unique, essentially non-contentious (hishō jiken - 非訟事件) nature of boundary determination suits. In such suits, the court exercises broad discretion and is not strictly bound by the parties' specific assertions (the Principle of Disposition applies less rigidly). As long as all interested co-owners are formally parties to the proceeding—whether as plaintiffs or defendants—they have the opportunity to participate and present their views, and a unified judgment binding on all can be rendered. Justice Chigusa emphasized, however, that this solution was specific to boundary suits and did not automatically grant general defendant standing to non-cooperative parties in other types of indispensable co-litigation. He also pointed out potential procedural complexities, such as the status of such a "defendant" if a plaintiff on their "side" were to die and this "defendant" inherited their position, or their alignment on appeal if both the original plaintiff group and the original defendant group appealed.

A Broader Shift: The Supreme Court Judgment of July 17, 2008 – Protecting the Right to Sue in Collective Rights Cases

A more significant and broadly applicable development occurred with the Supreme Court decision of July 17, 2008 (Minshu Vol. 62, No. 7, p. 1994). This case substantially expanded the permissibility of naming non-cooperative potential co-plaintiffs as defendants, particularly in the context of collective or common rights.

Facts of the 2008 Case: The lawsuit was initiated by some members of an iriai group (a traditional Japanese community holding common rights, 入会権 - iriaiken, to use certain land, often for forestry or foraging) against a third party. The plaintiffs sought a declaration that a specific parcel of land was iriaichi (入会地 - land subject to these common rights). Other members of the iriai group were unwilling to join the suit as co-plaintiffs. Traditionally, legal actions concerning the iriaiken itself (as a form of collective ownership, often characterized as sōyū - 総有) were considered to require all members of the iriai group to sue jointly as plaintiffs. This was based on the substantive law principle that such collective rights are managed and disposed of by the group as a whole (a principle affirmed in an earlier case, Supreme Court, November 25, 1966, Minshu Vol. 20, No. 9, p. 1921).

The 2008 Supreme Court Ruling: The Court held that if some members of a group holding such a collective right (like iriaiken) refuse to join a necessary lawsuit as plaintiffs, those members who do wish to sue can name the non-cooperative members as additional defendants, alongside the primary third-party defendant against whom the collective right is being asserted. As long as all members of the group are thereby made parties to the suit (whether as plaintiffs or defendants), the requirement of "joint litigation" for the purposes of party standing is considered fulfilled. The suit would not be dismissed for lack of standing simply because not all right-holders were on the plaintiff side.

Core Rationale of the 2008 Ruling: The central justification provided by the Supreme Court was the "protection of the right to sue (soken no hogo) of the members wishing to assert the common right." To hold that a few unwilling individuals could effectively block the entire group (or a substantial portion thereof) from seeking judicial redress for alleged infringements on its collective rights would be an unacceptable infringement of this fundamental right of access to justice. The Court reasoned that as long as all members are included as parties in some capacity, they have the opportunity to participate in the proceedings, and the resulting judgment, which will determine the status of the common right, can be made binding on all. This, in the Court's view, adequately protects the interests of the non-cooperative members (now defendants) while allowing the claim to be heard.

Conditional Nature of this "Protection of Right to Sue": It's important to note that subsequent analysis by judicial research officials associated with the Supreme Court has suggested that this "protection of the right to sue" rationale is not an absolute green light in all situations. It is seen as particularly compelling when there is a tangible risk that, if the lawsuit cannot be brought by including non-cooperative members as defendants, the collective right itself might be irreparably harmed or lost. This implies an element of necessity or a situation where this procedural workaround is effectively a "last resort" to prevent a substantive injustice – for instance, if there's a danger that the common land might be improperly transferred to a third party, perhaps even with the collusion of some non-cooperative members (which was an alleged factual background element in the 2008 case). Thus, the justification may be strongest where the non-cooperation actively endangers the collective right itself.

The Evolving Understanding of "Necessity of Joint Litigation" and "Uniformity of Judgment"

These Supreme Court decisions, particularly the 2008 judgment, reflect an evolution in the understanding of what "necessity of joint litigation" (soshō kyōdō no hitsuyō) and "uniformity of judgment" (gōitsu kakutei) mean in the context of indispensable necessary co-litigation.

From "Joint Institution of Action by Plaintiffs" (Teiso Kyōdō) to "Joint Participation by All as Parties" (Soshō Kyōdō):
- Traditional View (Stage 1): For rights that substantively required joint exercise (e.g., management and disposition of collectively owned property), the "necessity of joint litigation" was primarily understood as requiring all right-holders to join as co-plaintiffs. This was termed teiso kyōdō no hitsuyō (提訴共同の必要). Uniformity of judgment was then achieved concerning the ownership or status of that jointly held right.
- Intermediate Development (Stage 2 – Primarily for Internal Disputes or Procedurally-Based Indispensable Co-litigation): As discussed in Part 1 of this series, in certain types of indispensable co-litigation, particularly those arising from procedural needs (like actions to confirm the composition of an estate or to determine heirship status for subsequent estate division), it became accepted that indispensable parties could be on opposing sides of the lawsuit (e.g., some co-heirs as plaintiffs, others as defendants). In these scenarios, "joint litigation" evolved to mean that all necessary individuals were parties to the suit in some capacity, ensuring that the res judicata of the judgment would bind all of them on the common disputed issue. The strict requirement for all to be on the plaintiff side was relaxed because the substantive law didn't necessarily mandate joint exercise of a right against a third party in these contexts; rather, procedural law demanded a single, comprehensive resolution binding on all stakeholders.
- Modern Flexibility (Stage 3 – Extended to External Disputes with Non-Cooperative Co-Plaintiffs via the 2008 SC Ruling): The 2008 Supreme Court decision extends a similar flexibility (under the specific conditions of protecting the right to sue) even to disputes against external third parties involving traditionally collective rights. Even if substantive law might have historically suggested that all right-holders should act as joint plaintiffs to assert the collective right, procedural imperatives can justify allowing willing plaintiffs to bring in unwilling co-right-holders as defendants. The "necessity of joint litigation" is satisfied as long as all indispensable individuals are made parties to the action, ensuring they are subject to the court's jurisdiction and bound by its judgment.
The Evolved Meaning of "Uniformity of Judgment" (Gōitsu Kakutei):
In these more modern interpretations, "uniformity of judgment" does not strictly mean that all original right-holders must achieve the same plaintiff-side victory. Instead, it increasingly signifies that the court's determination on the core common issue (e.g., the existence and scope of the iriaiken, the composition of an estate, the status of an heir, the location of a boundary) is made in a single, consistent manner that is legally binding on all indispensable parties, regardless of their formal alignment as plaintiff or defendant within the lawsuit. The focus shifts from achieving uniformity of plaintiff action to achieving uniformity of the binding effect and consequences of the judgment on all essential stakeholders. This is crucial for ensuring that the judgment serves its purpose of providing a definitive and comprehensive resolution to the underlying dispute concerning the collective right or common interest.

Remaining Issues and Considerations

While the 2008 Supreme Court decision provided a significant pathway for overcoming the problem of non-cooperative co-plaintiffs in certain indispensable co-litigation scenarios, it also left some questions for future development:

Effect of the Judgment Between Co-Defendants: If non-cooperative potential co-plaintiffs are named as defendants alongside the original third-party defendant, what is the precise preclusive effect (e.g., res judicata) of the judgment on the common issue between these two categories of defendants? For true and complete uniformity of judgment, it is argued that the determination on the common right or issue should be binding among all parties, including between such co-defendants. If the litigation is viewed as a composite of an external dispute (the group versus the third party) and an internal dispute (cooperative members versus non-cooperative members concerning the assertion of the group's rights), then all relevant legal relationships concerning the core issue should ideally be resolved with binding effect on all participants.
Applicability to Claims for Performance: The 2008 Supreme Court case specifically involved a declaratory action (seeking confirmation of iriaichi status). Whether its reasoning—allowing non-cooperative co-plaintiffs to be named as defendants based on the "protection of the right to sue"—extends with equal force to claims for performance (e.g., a suit by some co-owners to recover possession of collectively owned property from a third party, when other co-owners are unwilling to join as plaintiffs) is a more complex question. Claims for performance directly seek to alter possession or compel action, and prior Supreme Court case law (e.g., Supreme Court, July 1, 1982, Minshu Vol. 36, No. 6, p. 891, concerning iriaiken) has historically been more restrictive about allowing individual members of a collective to bring performance claims concerning the collective right itself (as opposed to their individual rights of use derived from it). While the 2008 decision explicitly distinguished an earlier (1966) precedent that had mandated joint plaintiffship for iriaiken confirmation, thereby signaling a potential shift, its full implications for performance claims in similar non-cooperative scenarios remain an area for careful consideration and future judicial clarification.

Conclusion (Part 2)

The Japanese legal system's approach to indispensable necessary co-litigation, particularly concerning the challenge of non-cooperative potential co-plaintiffs, has demonstrated a significant evolution. While traditionally adhering to strict requirements for joint plaintiffship based on substantive law principles of collective rights management, the Supreme Court has increasingly recognized the paramount importance of protecting the fundamental right to sue.

Through key decisions, notably the 1999 ruling in boundary determination suits and, more broadly, the 2008 judgment in the context of iriaiken (common rights), a pragmatic solution has emerged: under certain conditions, primarily to prevent the frustration of legitimate claims and to ensure access to justice, unwilling but indispensable co-right-holders may be named as defendants. This ensures that all necessary parties are before the court, allowing for a judgment that is uniformly binding on the common issue. This development reflects a sophisticated balancing act between the ideals of collective action inherent in certain substantive rights and the procedural necessity of ensuring that such rights can be effectively vindicated in court, even in the face of internal dissent among the right-holders. The focus has subtly shifted from a rigid insistence on uniformity in how a suit is initiated (all as plaintiffs) to ensuring uniformity in how the judgment binds all essential parties, thereby achieving a comprehensive and final resolution.