Intervention in Japanese Lawsuits: How Can Third Parties Join Ongoing Litigation to Protect Their Interests?

Japanese Attorney at Law - Bengoshi L.L.

• 9 min read

Civil lawsuits are not always confined to the original plaintiffs and defendants. Often, the outcome of a dispute can significantly affect the rights or legal interests of third parties who were not initially part of the action. Japanese civil procedure provides several mechanisms for such third parties to "intervene" (訴訟参加 - soshō sanka) in ongoing litigation, allowing them to protect their interests, assert their own claims, or support one of افتhe existing litigants. Understanding these intervention procedures is crucial for any entity whose interests might be impacted by a lawsuit in Japan.

This article explores the main forms of third-party intervention—Auxiliary Intervention (hojo sanka), Independent Party Intervention (dokuritsu tōjisha sanka), and Joinder as a Co-Litigant through Intervention (kyōdō soshō sanka)—as well as the related concept of Notice of Lawsuit (soshō kokuchi).

I. Why Intervention? The Rationale Behind Third-Party Participation

Allowing third parties to join ongoing lawsuits serves several important functions within the Japanese civil justice system:

  1. Protecting Third-Party Interests: It provides a direct avenue for individuals or entities whose legal rights or obligations might be affected by the judgment to have their voices heard and to take steps to safeguard their positions.
  2. Ensuring Comprehensive and Consistent Dispute Resolution: By bringing all significantly interested parties into a single proceeding, courts can achieve a more holistic and consistent resolution of intertwined legal issues, avoiding piecemeal litigation and potentially conflicting outcomes.
  3. Judicial Economy: Dealing with related claims and interests in one consolidated action is generally more efficient for the courts and the parties involved than handling multiple separate lawsuits.

II. Auxiliary Intervention (Hojo Sanka): Supporting a Side

Auxiliary intervention is the most common form of third-party participation, allowing a third party to join a lawsuit to assist one of the existing litigants. It is governed by Articles 42 through 46 of the Code of Civil Procedure (CCP) (民事訴訟法 - Minji Soshō Hō).

An auxiliary intervenor (hojo sankanin) joins the lawsuit because they have a "legal interest" (hōritsujō no rigai kankei) in its outcome. Their purpose is to support one of the original parties (the "assisted party" – 被参加人 hi-sanka-nin) in achieving a favorable judgment, as this outcome will indirectly benefit the intervenor's own legal position.

This is the critical threshold for auxiliary intervention. The interest must be a legal one, not merely factual, economic, commercial, or sentimental. The outcome of the main lawsuit must have a direct or indirect legal consequence on the rights or duties of the third party seeking to intervene.

  • Examples of "Legal Interest":
    • A guarantor may intervene to support the principal debtor in a suit brought by a creditor, as a judgment against the debtor could lead to the guarantor's liability.
    • An insurer may intervene to support its insured who is being sued, as the insurer might be liable to indemnify the insured.
    • A sub-lessee may intervene to support their lessor (the original lessee) if the head lease is being challenged, as the sub-lessee's right to occupy depends on the validity of the head lease.
    • A person who has acquired property from one of the litigants, where the title to that property is at issue in the main suit.
  • Judicial Interpretation: Courts interpret "legal interest" based on whether the judgment in the main action will have a "reflex effect" (hansha-kō) on the intervenor's legal position or if the intervenor's legal status is a direct or indirect prerequisite or consequence of the judgment. A leading Supreme Court case (Judgment of February 16, 1973, Second Petty Bench, Minshū Vol. 27, No. 1, Page 79) dealt with whether an auxiliary intervenor in an original action could intervene in a subsequent retrial action, discussing the nature of the interest required.

C. Procedure for Intervention (CCP Art. 43)

A third party seeking to intervene as an auxiliary intervenor must file an application (申出 - mōshide) with the court where the main lawsuit is pending.

  • No formal court permission is required to file the application.
  • However, any of the original parties can raise an objection to the intervention. If an objection is lodged, the court will rule on the permissibility of the intervention (i.e., whether the "legal interest" requirement is met).

D. Status and Powers of an Auxiliary Intervenor (CCP Art. 45)

  • Broad Procedural Rights: An auxiliary intervenor can generally perform almost all procedural acts that the assisted party can perform. This includes submitting allegations and evidence, making motions, examining witnesses, and even filing an appeal against an unfavorable judgment, provided the assisted party does not object or has not already done so.
  • Limitations:
    • The intervenor's actions cannot contradict the procedural acts already taken by the assisted party (e.g., an intervenor cannot deny a fact already admitted by the assisted party).
    • The intervenor generally cannot take actions that are clearly disadvantageous to the assisted party.
    • Some acts, like withdrawal of the claim or a settlement that binds the assisted party, can only be done by the assisted party themselves.
    • If the assisted party's actions conflict with the intervenor's, the assisted party's actions usually take precedence, though there are complex exceptions where the intervenor's acts might be upheld if they are objectively necessary for defending the case and the assisted party is, for example, failing to act.

E. The "Intervention Effect" (Sankateki Kōryoku) (CCP Art. 46)

This is a crucial consequence of auxiliary intervention. The judgment rendered in the main lawsuit becomes binding between the auxiliary intervenor and the party they assisted in any subsequent legal disputes between them.

  • This means that the intervenor generally cannot, in a later dispute with the assisted party, contradict the findings of fact or law that were prerequisites to the main judgment (especially those points on which the assisted party lost, despite the intervenor's efforts).
  • It is similar in effect to res judicata but applies specifically to the relationship between the intervenor and the party they supported, regarding the reasoning of the main judgment. It aims to prevent the intervenor from re-litigating issues against the assisted party that were effectively determined through their joint (though perhaps unsuccessful) efforts in the main suit.

III. Independent Party Intervention (Dokuritsu Tōjisha Sanka): Asserting One's Own Claim

Independent party intervention, governed by CCP Articles 47 to 51, is a more profound form of intervention where a third party enters the lawsuit not merely to support an existing party, but to assert their own independent claims regarding the subject matter of the dispute, effectively becoming a main party and creating a three-sided (or multi-sided) lawsuit.

This type of intervention is available to a third party who claims that:

  1. The whole or part of the subject matter of the ongoing litigation is their own right; or
  2. Their own rights will be prejudiced or infringed by the outcome of the litigation between the original plaintiff and defendant.

The purpose is to allow a third party with a direct, primary claim to the dispute's core to have their rights adjudicated in the same proceeding, thus ensuring a comprehensive resolution and preventing conflicting judgments.

B. Types of Independent Party Intervention (CCP Art. 47(1))

  1. Intervention Claiming Right to the Subject Matter (権利主張参加 - kenri shuchō sanka):
    • The third party (intervenor) asserts that they, not the original plaintiff or defendant, are entitled to the property, debt, or other right that is the subject of the dispute between the original parties.
    • Example: Plaintiff A sues Defendant B for the return of a specific painting. Intervenor C files an independent party intervention claiming that C, not A or B, is the true owner of the painting and demands its return from whoever possesses it.
  2. Intervention to Prevent Infringement of One's Right (詐害防止参加 - sagai bōshi sanka):
    • The third party asserts that the judgment between the original plaintiff and defendant, if rendered as sought, will wrongfully prejudice their own distinct legal rights.
    • Example: Debtor D is being sued by Plaintiff P for a sum of money. Creditor C, who has a claim against D, fears that P and D might collude in the lawsuit (e.g., D admits P's claim without a real basis) to transfer D's assets to P, thereby defrauding C of their ability to recover from D. C might intervene to protect their creditor's rights by challenging the validity of P's claim against D.

C. Procedure for Intervention

The third party files an application for independent party intervention with the court. This application essentially takes the form of a new complaint, stating the intervenor's claims against one or both of the original parties. The court will then decide on the permissibility of the intervention based on whether the conditions in Article 47 are met.

D. Nature of the Resulting Litigation

If permitted, independent party intervention transforms the lawsuit into a tripartite (or multi-party) action. The intervenor becomes a full-fledged party. The claims of all three (original plaintiff, original defendant, and intervenor) are typically adjudicated together in a unified manner to ensure a consistent and comprehensive resolution of the intertwined rights and obligations. The relationship among the three parties often takes on characteristics similar to those in a necessary joinder (see below), requiring a single, coherent judgment.

IV. Joinder as a Co-Litigant through Intervention (Kyōdō Soshō Sanka) (CCP Art. 52)

This is a specialized form of intervention where a third person, for whom the subject matter of the litigation must be "uniformly determined" in relation to one of the original parties, can intervene as a co-plaintiff or co-defendant alongside that original party.

  • This often occurs in situations that would have constituted necessary joinder if all relevant persons had been parties from the beginning.
  • The intervening third party essentially joins to fulfill the requirements of necessary joinder (i.e., to ensure that all indispensable parties for a unified judgment are part of the suit). Their status and procedural rights are then governed by the rules applicable to necessary co-litigants.

V. Notice of Lawsuit (Soshō Kokuchi): Inviting Participation (CCP Art. 53)

Distinct from intervention initiated by a third party, the "notice of lawsuit" procedure allows an existing party to formally notify a third person about the pending litigation.

A. What is It?

A party to a lawsuit can give written notice of the suit to a third person who has a legal interest in its outcome and who might be entitled to intervene (typically as an auxiliary intervenor).

B. Purpose

  1. Opportunity to Intervene: It provides the notified third person with a clear opportunity to join the lawsuit as an auxiliary intervenor to protect their interests.
  2. Binding Effect (Even Without Intervention): Even if the notified person chooses not to intervene, the notice can have legal consequences for them in relation to the notifying party.

C. Effect of Notice (CCP Art. 53(4))

If the notified person (hi-kokuchi-sha) does not intervene, they are generally precluded, in any subsequent litigation between themselves and the notifying party (kokuchi-sha), from disputing the correctness of the findings of fact and law that were essential to the judgment in the notified lawsuit, provided these findings are also relevant to the subsequent dispute. This preclusive effect is similar to the "intervention effect" under Article 46 that applies to an auxiliary intervenor who does participate. It essentially extends some of the binding force of the judgment to the non-intervening notified party vis-à-vis the notifier, preventing them from re-litigating settled points.

VI. Comparing with Intervention in Common Law (e.g., U.S. FRCP Rule 24)

For context, U.S. federal procedure under FRCP Rule 24 distinguishes:

  • Intervention as of Right (Rule 24(a)): Permitted when a statute confers an unconditional right or when the applicant claims an interest relating to the subject of the action, and disposing of the action might impair their ability to protect that interest, unless existing parties adequately represent it. This has conceptual overlaps with situations warranting necessary joinder, strong grounds for auxiliary intervention where a direct legal interest is very clear, or independent party intervention where the intervenor's right is central.
  • Permissive Intervention (Rule 24(b)): May be permitted when a statute confers a conditional right or when the applicant's claim or defense shares a common question of law or fact with the main action. The court exercises discretion, considering undue delay or prejudice. This is broader and might cover situations where a Japanese court would find a "legal interest" for auxiliary intervention, or where a third party's claim is closely related but doesn't meet the stricter tests for independent party intervention.

While both systems aim to allow relevant third parties to join, the specific categories, tests, and the degree of judicial discretion differ.

VII. Strategic Considerations

  • For Existing Parties:
    • Consider whether giving a soshō kokuchi to potentially interested third parties is strategically advantageous (e.g., to bind them to the outcome, to encourage their support as an auxiliary intervenor, or to preempt future disputes).
    • If a third party applies to intervene, carefully assess whether their stated grounds meet the legal requirements and whether to file an objection.
  • For Potential Intervenors:
    • Proactively monitor litigation that might affect your legal interests.
    • If your rights are implicated, promptly assess whether you meet the criteria for auxiliary intervention (to support a side and gain the protection of the intervention effect) or independent party intervention (to assert your own primary claim).
    • Weigh the significant benefits of participating (influencing the outcome, directly protecting rights) against the costs, time, and burdens of becoming involved in litigation.
    • Timeliness of an intervention application is important; undue delay can be a factor in the court's decision, especially for independent party intervention.

VIII. Conclusion

Intervention mechanisms in Japanese civil procedure provide essential pathways for third parties whose rights or legal interests are intertwined with ongoing litigation to step in and protect those interests. Auxiliary intervention allows a third party to support an existing litigant, primarily to safeguard their own derivative legal position. Independent party intervention, a more profound step, allows a third party to assert their own primary claims concerning the very subject matter of the dispute, transforming the litigation into a multi-polar contest. Furthermore, the notice of lawsuit procedure serves to formally link interested third parties to the litigation and its outcome, even if they choose not to actively participate.

A clear understanding of these distinct but related procedures is vital for any individual or entity that might be affected by, or find it necessary to engage with, Japanese civil proceedings beyond the original set of litigants. These tools are designed to achieve more comprehensive, consistent, and ultimately just resolutions to complex, multi-faceted disputes.