Multiple Parties, One Lawsuit: How Does "Joinder of Parties" (共同訴訟) Work in Japan?

Japanese Attorney at Law - Bengoshi L.L.

• 8 min read

Modern business disputes are rarely simple one-on-one affairs. Often, multiple claimants may have related grievances against a single defendant, or a single plaintiff might have claims against several defendants whose actions are intertwined. Japanese civil procedure provides a mechanism to handle such multi-party scenarios efficiently and consistently through "Joinder of Parties," known as Kyōdō soshō (共同訴訟). This allows multiple plaintiffs to sue together, or multiple defendants to be sued together, in a single lawsuit, provided certain conditions are met. Understanding the types of joinder and their respective procedural rules is crucial for businesses facing complex, multi-faceted legal conflicts in Japan.

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

A. Definition and Purpose

Kyōdō soshō refers to a situation where two or more persons are joined as plaintiffs or as defendants in a single lawsuit. The primary purposes of allowing joinder of parties are:

  1. Judicial Economy: To resolve related claims involving multiple parties in a single proceeding, thereby saving time, costs, and judicial resources compared to multiple separate lawsuits.
  2. Prevention of Inconsistent Judgments: To avoid the risk of contradictory rulings that might arise if related claims involving different parties were litigated separately.
  3. Procedural Guarantee and Convenience for Parties: To provide a more convenient and comprehensive forum for all interested parties to have their interconnected rights and obligations adjudicated together.

B. General Distinction: Permissive Joinder vs. Necessary Joinder

Broadly, joinder of parties in Japan can be categorized into two main types, based on whether the joinder is optional (permissive) or mandatory (necessary) for the proper adjudication of the dispute:

  • Ordinary Joinder (Tsūjō kyōdō soshō 通常共同訴訟): This is a form of permissive joinder, where parties may be joined if their claims or liabilities are sufficiently connected.
  • Necessary Joinder (Hitsuyō-teki kyōdō soshō 必要的共同訴訟): This involves situations where the nature of the dispute is such that all relevant parties must be joined for a consistent and effective judgment.

II. Ordinary Joinder (Tsūjō kyōdō soshō - 通常共同訴訟) (Code of Civil Procedure, Art. 38)

Ordinary joinder allows multiple plaintiffs or multiple defendants to be parties to a single lawsuit if their respective rights, obligations, or the causes of action meet certain criteria of relatedness.

A. When is Ordinary Joinder Permitted? Requirements under Article 38

Article 38 of the Code of Civil Procedure (Minji Soshō Hō 民事訴訟法) sets out the conditions under which persons may sue or be sued as co-litigants:

  1. Commonality of Rights or Obligations (権利義務共通 - Kenri gimu kyōtsū):
    • When the rights or obligations that are the subject matter of the litigation are common to two or more persons.
    • Example: Multiple co-owners of a property suing for trespass.
  2. Same Factual and Legal Cause (同一の事実上及び法律上の原因 - Dōitsu no jijitsu-jō oyobi hōritsu-jō no gen'in):
    • When the rights or obligations of the co-litigants arise from the same factual circumstances and the same legal grounds.
    • Example: Multiple passengers injured in the same accident suing the same transportation company.
  3. Same Kind of Rights/Obligations AND Same Kind of Factual/Legal Cause (権利義務同種かつ原因同種 - Kenri gimu dōshu katsu gen'in dōshu):
    • This third category, introduced by an amendment to the Code, broadens the scope of permissible joinder. It allows joinder if:
      • The rights or obligations are of the "same kind" (e.g., all claims are for monetary damages based on contract, even if the contracts are separate).
      • AND these rights or obligations arise from factually and legally the "same kind of cause" (e.g., multiple customers suing a manufacturer for defects in the same line of products purchased under similar, though separate, contracts).
    • This aims to encompass situations where there's a strong commonality in the type of dispute, even if not strictly the "same" single transaction or event.

B. Procedural Treatment: The Principle of Independence of Co-Litigants (Kyōdō soshō'nin dokuritsu no gensoku - 共同訴訟人独立の原則) (Code of Civil Procedure, Art. 39)

In an ordinary joinder, the general rule is that each co-litigant acts independently of the others. Article 39 states: "Any act performed by one of the co-litigants, or any act performed by an opposing party against one of the co-litigants, or any matter that has arisen with regard to one of the co-litigants shall not affect the other co-litigants."

  • Independent Action: Each co-plaintiff or co-defendant can make their own allegations, present their own evidence, make admissions, settle their part of the claim, or appeal independently.
  • No Binding Effect of One's Actions on Others: An admission made by one co-defendant does not bind other co-defendants. A settlement by one co-plaintiff does not terminate the claims of others.
  • Exceptions and Nuances:
    • Advantageous Acts: An act performed by one co-litigant that is objectively advantageous to all (e.g., successfully proving a fact that benefits all co-plaintiffs' claims) can be utilized by the court for the benefit of all.
    • Common Objections: Certain objections raised by one co-litigant, such as a challenge to the court's jurisdiction, may, if successful, lead to the dismissal or transfer of the entire case affecting all.
    • Evidence: Evidence submitted by one party becomes part of the record and can be considered by the court in relation to all parties (shōko kyōtsū no gensoku 証拠共通の原則 – principle of commonality of evidence).

C. Examples in Business Litigation:

  • Several unrelated creditors whose claims against a single debtor arise from the "same kind of factual and legal cause" (e.g., multiple suppliers with unpaid invoices for similar goods delivered under similar terms).
  • A patent holder suing multiple unrelated companies for allegedly infringing the same patent through separate acts.
  • A group of employees suing their employer for similar wage claims arising under the same kind of employment contracts and company policies.

III. Necessary Joinder (Hitsuyō-teki kyōdō soshō - 必要的共同訴訟) (Code of Civil Procedure, Art. 40)

Necessary joinder applies to situations where the nature of the legal relationship or the subject matter of the dispute is such that a single, unified judgment binding on all relevant persons is essential for an effective and legally sound resolution.

A. Definition and Rationale: The Need for a Unified Judgment (Gōitsu kakutei no hitsuyō-sei - 合一確定の必要性)
In these cases, the rights and obligations are so interconnected that separate, potentially conflicting, judgments against different parties would be legally untenable or practically meaningless. Therefore, all persons whose rights are to be jointly determined must be joined in the litigation, and the judgment must be uniform for all of them.

B. Types of Necessary Joinder:

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

  1. Indispensable (Proper) Necessary Joinder (Koyū hitsuyō-teki kyōdō soshō - 固有必要的共同訴訟):
    • Nature: This is where substantive law dictates that the legal relationship in question can only be determined jointly with respect to all persons involved. The joinder of all such persons is a prerequisite for the court to properly adjudicate the claim.
    • Consequence of Non-Joinder: Failure to join all indispensable parties can lead to the dismissal of the action for lack of proper parties (tōjisha tekikaku 当事者適格 – standing to sue/be sued). The court cannot render a valid judgment without all of them.
    • Examples:
      • An action for the partition of co-owned property: all co-owners must be parties.
      • A lawsuit concerning the rights and obligations of all members of a Japanese civil law partnership (kumiai 組合) with regard to partnership property or collective liabilities.
      • Certain actions to nullify corporate acts where specific statutes require joinder of all relevant entities (e.g., an action to nullify a merger might require both merging companies as parties).
      • Actions to confirm a boundary between land parcels: owners of both parcels must be involved.
  2. Quasi-Necessary Joinder (Ruiji hitsuyō-teki kyōdō soshō - 類似必要的共同訴訟):
    • Nature: In these situations, while each potential co-litigant might theoretically be able to sue or be sued independently regarding their individual interest, if they are joined in a single lawsuit, the nature of their interconnected rights or the desired outcome necessitates a unified judgment to avoid logically inconsistent results.
    • Procedural Requirement for Unity: The substantive right might be individually determinable, but if these parties are brought together in one suit, procedural rules mandate that their case be handled in a unified manner to ensure a single, consistent outcome among them.
    • Examples:
      • Multiple beneficiaries of a trust suing a trustee for a breach of trust that uniformly affects all their interests.
      • Co-heirs involved in a lawsuit to confirm their respective shares or rights in inherited property.
      • A lawsuit by multiple shareholders challenging the validity of a particular corporate action that affects them all in the same way (though many such shareholder actions are often structured as indispensable necessary joinder regarding the company as a defendant).

C. Procedural Treatment under Article 40 CCP (Special Rules for Unified Proceedings):
Because a unified judgment is essential in necessary joinder, Article 40 of the Code of Civil Procedure provides special rules that deviate from the principle of co-litigant independence:

  • Acts by One Co-Litigant (Art. 40(1)): A procedural act performed by one necessary co-litigant (e.g., filing an appeal, making an admission) is effective for or against all co-litigants only if it is advantageous to all of them. An act by one that is disadvantageous to the others (e.g., one co-defendant admitting the plaintiff's claim) does not bind the other non-consenting co-litigants.
  • Acts by the Opposing Party (Art. 40(2)): An act performed by the opposing party directed towards one necessary co-litigant is deemed effective towards all of them.
  • Suspension or Interruption of Proceedings (Art. 40(3)): If grounds for suspension or interruption of the court proceedings arise with respect to one necessary co-litigant (e.g., death, bankruptcy), the proceedings are suspended or interrupted for all of them.
  • No Separate or Conflicting Judgments: The judgment must be a single, uniform decision binding on all necessary co-litigants. It is not possible to have different outcomes for different parties within the group of necessary co-litigants.

IV. Distinctions from Other Multi-Party Procedures

Joinder of parties should be distinguished from other mechanisms for involving multiple parties in a lawsuit:

  • Intervention (Soshō sanka 訴訟参加):
    • Assistant Intervention (Hojo sanka 補助参加): A third party with a legal interest in the outcome of a pending lawsuit joins to assist one of the existing parties.
    • Independent Party Intervention (Dokuritsu tōjisha sanka 独立当事者参加): A third party whose rights may be prejudiced by the outcome of a pending lawsuit, or who claims a right to the subject matter of the litigation, joins as an independent party.
      These involve third parties entering an existing lawsuit, whereas joinder of parties typically concerns the initial composition of plaintiffs or defendants, or the consolidation of separate but related cases.

V. Strategic Considerations for Businesses

  • Efficiency vs. Complexity: Joinder can significantly enhance efficiency by resolving multiple related claims in a single action. However, it can also increase the complexity of the proceedings, especially with numerous parties who might have slightly divergent interests or strategies, particularly in ordinary joinder.
  • Ensuring All Necessary Parties are Joined (for Necessary Joinder): For plaintiffs initiating actions that constitute indispensable necessary joinder, meticulous identification and inclusion of all required parties is crucial. Failure to do so can lead to dismissal.
  • Managing Co-Litigant Relationships: Especially in necessary joinder, where the actions of one can affect all (if advantageous), coordination among co-litigants regarding strategy, pleadings, and evidence can be vital, though sometimes challenging if their underlying interests are not perfectly aligned.
  • Jurisdictional Considerations: When joining multiple defendants, ensure that the chosen court has jurisdiction (territorial, subject-matter, and international, if applicable) over all of them, or that jurisdiction can be established through agreement or appearance.

Conclusion

Joinder of parties, or Kyōdō soshō, is a fundamental and versatile feature of Japanese civil procedure designed to manage lawsuits involving multiple claimants or defendants in a fair and efficient manner. A clear understanding of the distinction between ordinary joinder, which operates under the principle of co-litigant independence, and the more stringent necessary joinder, which demands unified adjudication for all involved, is critical for businesses. This knowledge allows for effective navigation of complex multi-party disputes, ensures that all proper parties are brought before the court when required, and enables informed strategic planning for litigation in Japan.