Joinder of Parties (Kyōdō Soshō) in Japanese Civil Litigation: When Can or Must Multiple Plaintiffs/Defendants Be Grouped?

Japanese Attorney at Law - Bengoshi L.L.

• 9 min read

Litigation frequently involves more than a simple one-on-one dispute; multiple plaintiffs may have similar grievances against a single defendant, a single plaintiff might have claims against several defendants, or various combinations thereof. Japanese civil procedure accommodates such multi-party scenarios through the doctrine of "Joinder of Parties" or "Co-litigation" (共同訴訟 - kyōdō soshō). Understanding when parties can be joined permissively and when they must be joined for a valid adjudication is crucial for structuring lawsuits effectively and avoiding procedural dismissals.

This article explores the two main types of joinder of parties in Japan—Ordinary Joinder (tsūjō kyōdō soshō) and Necessary Joinder (hitsuyō-teki kyōdō soshō)—their respective requirements, the status of co-litigants, and the strategic implications for those involved in Japanese civil disputes.

I. Understanding Joinder of Parties (Kyōdō Soshō) in Japanese Civil Procedure

A. What is Kyōdō Soshō?

Kyōdō soshō refers to a situation where a single lawsuit involves multiple parties on the plaintiff's side, the defendant's side, or both. This is also known as "subjective joinder of claims," as opposed to "objective joinder of claims" (請求の併合 - seikyū no heigō), where a single plaintiff asserts multiple claims against a single defendant.

The primary aims of allowing and sometimes requiring joinder of parties are:

  1. Judicial Economy: Resolving related claims involving multiple parties in a single proceeding is generally more efficient than conducting numerous separate lawsuits.
  2. Preventing Conflicting Judgments: Joinder can help avoid the risk of inconsistent or contradictory judgments that might arise if related matters concerning multiple parties were litigated separately.
  3. Comprehensive Dispute Resolution: It facilitates a more holistic resolution of interconnected disputes.

II. Ordinary Joinder (Tsūjō Kyōdō Soshō): Permissive Grouping

Ordinary joinder, governed by Article 38 of the Code of Civil Procedure (CCP) (民事訴訟法 - Minji Soshō Hō), allows multiple parties to be joined in a lawsuit if their claims or defenses are sufficiently related, but their participation as a group is not strictly mandatory for the validity of the action concerning each individual.

A. Legal Basis: CCP Article 38

Article 38 provides two main grounds for ordinary joinder:

  1. "Where the rights or obligations that are the subject matter of litigation are common to those several persons."
    • Example: Co-owners of a piece of property jointly suing a third party for its return, or all beneficiaries of a trust jointly suing the trustee for breach of fiduciary duty.
  2. "Where the rights or obligations that are the subject matter of litigation arise from the same factual and legal cause."
    • Example: Multiple passengers injured in the same bus accident suing the bus company for damages (same accident, similar legal basis of negligence). Several individuals who were allegedly defrauded through the same investment scheme suing the perpetrator.

(Note: An older version of Article 38 included a third, broader ground relating to "rights or obligations of the same kind based on the same kind of factual and legal causes." This was removed, and its underlying rationale is now largely covered by the existing two grounds or by other procedural mechanisms like subjective additional joinder or specialized collective action frameworks.)

B. The Principle of Independence of Co-Litigants (Kyōdō Soshōnin Dokuritsu no Gensoku)

A defining feature of ordinary joinder is the Principle of Independence of Co-Litigants, enshrined in CCP Article 41:
"The procedural acts of one co-litigant, or matters that have arisen with regard to one co-litigant, shall not affect the other co-litigants."

  • General Rule: Each co-plaintiff or co-defendant in an ordinary joinder essentially litigates their own case independently within the joint proceeding.
    • An admission made by one co-defendant does not bind other co-defendants.
    • The failure of one co-plaintiff to submit evidence does not prevent another co-plaintiff from doing so.
    • One co-litigant can withdraw their claim or defense, or file an appeal, irrespective of the others.
  • Exceptions/Modifications to Independence: This principle is not absolute and is tempered by doctrines designed to ensure fairness and efficiency:
    • Principle of Commonality of Allegations (Shuchō Kyōtsū no Gensoku): A factual allegation made by one co-litigant that is favorable to another co-litigant on the same side can be utilized by the court for the benefit of that other co-litigant, even if they didn't explicitly make the same allegation.
    • Principle of Commonality of Evidence (Shōko Kyōtsū no Gensoku): Evidence properly submitted by one co-litigant can be used by the court when assessing the claims or defenses of all other co-litigants involved in the joint proceeding, whether it benefits or prejudices them. This means parties cannot selectively "wall off" evidence introduced by their co-parties. (This principle is noted in Part 5 of the provided PDF snippets).

C. Procedural Management

In ordinary joinder, the court has discretion to separate the proceedings for different co-litigants if it deems necessary for efficiency or to avoid prejudice (CCP Art. 152, Para. 2). It is also possible for the court to render separate judgments concerning individual co-litigants at different times if their claims/defenses are severable and ripe for decision.

III. Necessary Joinder (Hitsuyō-teki Kyōdō Soshō): Mandatory Grouping for Unified Judgment

Necessary joinder, governed by CCP Article 40, applies to situations where the nature of the legal dispute is such that a single, consistent judgment must be rendered with respect to all indispensable parties involved. The primary rationale is the need for "unified adjudication" (合一確定 - gōitsu kakutei) to avoid legally or practically untenable outcomes.

A. Legal Basis: CCP Article 40

Article 40 states:
"(1) Where a judgment is required to be uniformly binding with regard to several persons, such persons shall be joined as co-plaintiffs or co-defendants.
(2) The provision of the preceding paragraph shall also apply where several persons are to jointly sue or be sued by reason of the same cause."

B. Types of Necessary Joinder

Japanese legal doctrine distinguishes between two main types of necessary joinder:

  1. Proper Necessary Joinder (Koyū Hitsuyō-teki Kyōdō Soshō):
    • Nature: This is the strictest form, arising when the right to sue or be sued itself (party qualification – 当事者適格 tōjisha tekkaku) is vested jointly and inseparably in all members of the group. All such persons must participate as co-litigants for the lawsuit to be properly constituted.
    • Examples:
      • Lawsuits concerning the administration or disposition of partnership property that require action by or against all partners collectively.
      • An action by a co-owner to seek the cancellation of a registration that affects the entire co-owned property, often requiring all co-owners to join as plaintiffs.
      • An action to nullify a shareholder resolution, where the company is the defendant (CCP Art. 831). If multiple shareholders seek nullification through separate suits that are later consolidated, their status might resemble this.
      • Certain types of status-altering lawsuits (keisei soshō – formative actions) that necessarily affect a legal relationship common to a defined group (e.g., a suit to determine the boundaries between commonly held parcels of land).
    • Consequences of Non-Joinder: If a party who is indispensable under proper necessary joinder is not included, the lawsuit may be dismissed for lack of proper parties (lack of party qualification).
    • Procedural Acts: Generally, all procedural acts, such as filing the lawsuit, appealing a judgment, withdrawing the action, or entering into a settlement, must be done by or with the consent of all proper necessary co-litigants.
  2. Quasi-Necessary Joinder (Ruiji Hitsuyō-teki Kyōdō Soshō):
    • Nature: This form arises when, although each individual member of the group might theoretically have the capacity to sue or be sued independently regarding their own interest, the nature of the underlying legal relationship or the effect of the judgment necessitates a uniform outcome for all involved to avoid practical absurdities or ensure the judgment's effectiveness. The judgment in such cases often has an effect that extends to others in the group even if they are not formal parties from the outset (though they may often be brought in via intervention or consolidation).
    • Examples:
      • A shareholder derivative action, where if one shareholder sues on behalf of the company, the outcome is binding on the company and thus indirectly on other shareholders. If other shareholders intervene or file similar suits that are then consolidated, their joinder has characteristics of quasi-necessary joinder.
      • Certain actions by one creditor that have an effect on the rights of other creditors in a collective proceeding (e.g., some actions in bankruptcy).
    • Procedural Handling: While an action might be initiated by one person, the proceedings are structured and managed to ensure that the final judgment is consistent for all those whose rights are inextricably linked. Other affected individuals often have rights to intervene or may be joined.

C. Status and Conduct of Co-Litigants in Necessary Joinder

The Principle of Independence of Co-Litigants (CCP Art. 41) is largely inapplicable in cases of necessary joinder. Instead:

  • Acts by One Co-Litigant (CCP Art. 40, Para. 3 & 4):
    • A procedural act undertaken by one necessary co-litigant that is advantageous to the common cause (e.g., submitting favorable evidence, successfully appealing an adverse ruling) generally benefits all other co-litigants.
    • However, procedural acts by one co-litigant that are detrimental (e.g., making an unfavorable admission, withdrawing the claim, failing to appeal) generally do not bind the other co-litigants unless they all consent or similarly act. This is to protect the integrity of the joint right or interest.
    • An appeal filed by one necessary co-litigant has the effect of an appeal for all.
  • Unified Trial and Judgment: The entire case must proceed as a single, indivisible unit. Only one consistent judgment can be rendered, which is uniformly binding on all necessary co-litigants.

IV. Adding Parties to Ongoing Litigation: Subjective Additional Joinder (Shukanteki Tsuikateki Heigō)

CCP Article 39 provides a mechanism for adding a third person as a co-plaintiff or co-defendant to a pending lawsuit. This "subjective additional joinder" is permissible if the conditions for ordinary joinder under CCP Article 38 would be met with respect to the relationship between the existing parties and the person to be added. If the person is to be added as a co-plaintiff, their consent is generally required.

V. Comparing with Joinder Rules in Common Law (e.g., U.S. FRCP Rules 19 & 20)

For those familiar with U.S. federal procedure:

  • Permissive Joinder (FRCP Rule 20) vs. Ordinary Joinder (Tsūjō Kyōdō Soshō):
    • FRCP Rule 20 allows permissive joinder of plaintiffs if they assert rights arising out of the "same transaction, occurrence, or series of transactions or occurrences" AND a "question of law or fact common to all plaintiffs will arise." A similar test applies for joining defendants.
    • Japan's CCP Article 38 (rights/obligations are "common" OR arise from "same factual and legal cause") has a similar purpose of promoting efficiency and consistency. While the wording differs, both aim to group related but not necessarily interdependent claims.
  • Required Joinder of Parties (FRCP Rule 19) vs. Necessary Joinder (Hitsuyō-teki Kyōdō Soshō):
    • FRCP Rule 19(a) identifies "Persons Required to be Joined if Feasible" if their absence would prevent complete relief among existing parties, or if their absence might impair their own ability to protect their interest or leave existing parties subject to a substantial risk of incurring multiple or inconsistent obligations. If such a person cannot be joined, Rule 19(b) considers whether they are "indispensable," in which case the action might be dismissed.
    • Japan's concept of necessary joinder, particularly "proper necessary joinder," shares the underlying rationale of ensuring that all indispensable parties are before the court for a just and effective adjudication. The distinction between "proper" (where party qualification itself is joint) and "quasi-necessary" (where unified judgment is needed for other reasons) provides a slightly different doctrinal framing, but the goal of achieving a binding and consistent outcome for all essential stakeholders is similar.

VI. Strategic Considerations for Litigants

  1. Initiating Suit – Assessing Who to Include:
    • When contemplating litigation with multiple potential plaintiffs or defendants, carefully analyze if the conditions for ordinary joinder are met. Weigh the strategic benefits of a consolidated action (e.g., cost savings, consistent findings) against potential complexities (e.g., managing diverse interests, slower pace).
    • Critically, determine if any parties are necessary co-litigants. Failure to join a party required for proper necessary joinder can lead to dismissal.
  2. Managing Ordinary Co-Litigation:
    • If you are one of several ordinary co-litigants, remember the Principle of Independence. Your procedural acts generally won't bind others, and vice versa. However, be mindful of the principles of commonality of allegations and evidence.
    • Strategic coordination with co-litigants on the same side can still be highly beneficial, even if not legally required.
  3. Navigating Necessary Co-Litigation:
    • This requires a much higher degree of coordination. Since advantageous acts by one can benefit all, and detrimental acts (like admissions or withdrawal) by one generally don't bind others without consent, a unified strategy is paramount.
    • Understand that the entire case will be treated as a single unit, culminating in one indivisible judgment.
  4. Responding to or Seeking Joinder:
    • If an opponent seeks to join you or another party to an ongoing suit, or if you believe another party should be added, carefully assess whether the criteria for ordinary or (if applicable) necessary joinder are met.

VII. Conclusion

Joinder of parties (kyōdō soshō) is a fundamental and intricate aspect of Japanese civil procedure, designed to facilitate the fair, efficient, and consistent resolution of disputes involving multiple claimants or defendants. The critical distinction between ordinary joinder, where co-litigants largely maintain their procedural independence, and necessary joinder, which demands unified participation and judgment due to the inseparable nature of the legal interests involved, has profound implications for how lawsuits are structured and managed.

A thorough understanding of when parties can be permissively grouped versus when they must be mandatorily included is essential for any litigant in Japan. It helps in avoiding procedural dismissals, ensuring that judgments are effective against all appropriate parties, and strategically navigating the complexities of multi-party litigation.