"Assumption of Litigation" (Soshō Hikiuke) in Japan: How Can a Third-Party Successor Be Forced to Join or Voluntarily Take Over a Lawsuit?

Japanese Attorney at Law - Bengoshi L.L.

• 9 min read

While previous articles have explored how third parties might voluntarily intervene in ongoing Japanese lawsuits to protect their interests, what happens if a crucial legal interest—the very right or obligation being litigated—is transferred to a third party during the proceedings, and that successor doesn't choose to join? Japanese civil procedure provides a mechanism known as "Assumption of Litigation" (訴訟引受け - soshō hikiuke) which allows an existing party to, in effect, compel such a third-party successor to become a party to the pending lawsuit.

This article delves into this important, though perhaps less frequently encountered, procedural tool, explaining how it works for successors to both rights and obligations, its requirements, its effects, and how it differs from voluntary intervention by a successor.

I. Understanding "Assumption of Litigation" (Soshō Hikiuke): Compelling Joinder

A. Core Concept and Rationale

Soshō hikiuke is a procedure outlined in Articles 50 and 51 of Japan's Code of Civil Procedure (CCP) (民事訴訟法 - Minji Soshō Hō). It allows an existing party to a lawsuit to file a motion with the court to have a third person—who has succeeded to the specific right or obligation that is the subject matter of the litigation during its pendency—take over or join the lawsuit concerning that succeeded interest.

The primary rationales for this mechanism are:

  1. Ensuring Judgments Bind the True Interest Holder: It aims to ensure that the lawsuit proceeds with, and the ultimate judgment is binding upon, the actual current holder of the disputed right or obligation.
  2. Promoting Finality and Preventing Evasion: It prevents an original party from frustrating the litigation or evading the consequences of a judgment by simply transferring the disputed interest to a third party while the suit is ongoing.
  3. Judicial Economy: It allows for the resolution of the dispute concerning the transferred interest within the existing proceedings, rather than potentially requiring a new lawsuit against the successor.

B. Distinguishing from Voluntary Intervention by a Successor (Sanka Shōkei - CCP Art. 49)

It's crucial to distinguish soshō hikiuke from sanka shōkei (Intervention by a Successor) under CCP Article 49:

  • Sanka Shōkei (Art. 49): This is when the third-party successor to the disputed right or obligation voluntarily applies to the court to intervene in the lawsuit to assert their succession and protect their interests. The initiative comes from the successor.
  • Soshō Hikiuke (Arts. 50, 51): This is when an existing party to the lawsuit takes the initiative to file a motion to bring in or compel the joinder of the third-party successor. The initiative comes from a party already in the suit.

While both deal with successors to the litigated interest, the procedural impetus is different.

II. Assumption of Suit by a Successor to a Disputed Right (CCP Art. 50)

CCP Article 50 addresses the scenario where a third party succeeds to the right that is the subject matter of the lawsuit.

A. When Applicable

This provision applies when, during the pendency of a lawsuit, a third party takes over (e.g., through assignment, sale, or other transfer) all or part of the right being claimed by the plaintiff or asserted by the defendant as their own (for instance, in a property ownership dispute).

  • Example 1: Plaintiff A is suing Defendant B for payment of a JPY 10 million debt. During the lawsuit, Plaintiff A assigns this JPY 10 million claim to Third Party C.
  • Example 2: Plaintiff P is suing Defendant D for title to a piece of real estate. During the suit, Defendant D sells their asserted interest in the property to Third Party T.

B. Who Can Apply?

The motion for assumption of suit under Article 50 can be filed by the party opposing the one whose right was transferred.

  • In Example 1 above, Defendant B (who is being sued by Plaintiff A for the debt now owned by C) can file a motion to have Third Party C assume the lawsuit as the plaintiff.
  • In Example 2, Plaintiff P (who is suing Defendant D for title to property now claimed by T) could file a motion to have Third Party T assume or join the lawsuit regarding the property.

C. Procedure

The existing party files a motion with the court. The court will typically hear from all involved (the applicant, the original party whose right was transferred, and the third-party successor) before deciding whether to issue an order compelling the assumption of the suit (CCP Art. 50(2)). The third-party successor can raise objections, for instance, by disputing the validity or scope of the alleged succession.

D. Effect on the Original Party (CCP Art. 50(3))

If the court orders the third-party successor to assume the suit, the party who made the application (the original opponent of the party whose right was transferred) can then apply to the court to have the original party (the transferor) withdraw from the litigation with respect to the succeeded right.

  • If the original party is permitted to withdraw, the successor effectively takes their place in the lawsuit concerning that specific right.
  • If the original party does not withdraw (e.g., if the transfer was partial, or if withdrawal is not sought or granted), both might remain, potentially creating a co-litigant relationship.

III. Assumption of Suit by a Successor to a Disputed Obligation (CCP Art. 51)

CCP Article 51 addresses the scenario where a third party succeeds to the obligation that is the subject matter of the lawsuit.

A. When Applicable

This applies when, during the pendency of a lawsuit, a third party takes over the obligation that the plaintiff is seeking to enforce against the original defendant.

  • Example: Plaintiff X is suing Defendant Y for performance of a contractual obligation (e.g., delivery of goods). During the suit, Third Party Z contractually assumes Defendant Y's obligation to deliver those goods to Plaintiff X.

B. Who Can Apply?

The motion for assumption of suit under Article 51 can be filed by the plaintiff (the party to whom the obligation is owed).

C. Procedure

Similar to Article 50, the plaintiff files a motion, and the court decides after hearing the relevant parties.

D. Effect on the Original Defendant

A key difference from Article 50 is that Article 51 does not explicitly provide a mechanism for the plaintiff to apply for the withdrawal of the original defendant after the successor assumes the obligation.

  • This reflects the substantive law of obligations. If the third party's assumption of the debt was "cumulative" or "adjunctive" (heizon-teki saimu hikiuke), meaning the original debtor (original defendant) remains liable alongside the new assuming party, the plaintiff would generally want to keep both in the lawsuit.
  • If the assumption was an "exempting" or "discharging" assumption of debt (menseki-teki saimu hikiuke), where the original debtor is fully released from the obligation (which usually requires the creditor's consent under substantive law), then the original defendant might be able to seek their own dismissal from the suit by proving these facts. However, the plaintiff cannot unilaterally remove them via Article 51 in the same way an applicant under Article 50 can seek the withdrawal of the original transferor of a right.

E. Scope of "Succession to Obligation"

There has been doctrinal debate on whether Article 51 applies only to exempting assumptions of debt. The prevailing view and court practice tend to limit its application primarily to situations where the original obligor is intended to be replaced, or at least where the successor takes on the primary obligation. Compelling a merely cumulative debtor to join under Article 51 is less straightforward, though not entirely ruled out by all commentators if it serves procedural efficiency.

IV. Requirements for an Order of Assumption

For a court to order assumption of litigation under either Article 50 or 51, the following conditions generally need to be met:

  1. The lawsuit must be currently pending before the court.
  2. The third party must have "succeeded" (shōkei shita) to all or part of the specific right or obligation that is the subject matter of the litigation during its pendency.
    • "Succession" can occur through various legal acts such as assignment of a claim, sale of disputed property, inheritance (though death is primarily handled by interruption/takeover rules), or certain types of corporate reorganizations like a company demerger/spin-off if specific disputed rights/obligations are clearly transferred to a successor entity.
    • The fact and validity of the succession itself must be proven to the court by the party making the motion.
  3. A valid motion must be filed by the entitled existing party (the opponent of the transferor of a right under Art. 50, or the plaintiff in the case of succession to an obligation under Art. 51).

The court will issue a formal decision (決定 - kettei) on the motion, against which an immediate appeal (即時抗告 - sokuji kōkoku) can typically be filed.

Once an order for assumption of litigation becomes final and binding:

  • Successor Becomes a Party: The third-party successor acquires the status of a party to the litigation with respect to the succeeded interest. They can make allegations, submit evidence, and participate fully in the proceedings.
  • Binding Effect of Prior Proceedings: The successor is generally bound by the procedural acts and evidence in the record up to the point of their assumption, to the extent consistent with due process and their ability to now protect their interests. They cannot simply rewind the clock and start everything afresh.
  • Relationship with the Original Party:
    • If the original party whose interest was succeeded to is permitted to withdraw (more straightforward under Art. 50(3)), the successor effectively substitutes them.
    • If the original party does not withdraw (often the case under Art. 51, or if withdrawal is not sought/granted under Art. 50), both the original party and the successor may remain as co-litigants. Their relationship might then be akin to a form of necessary joinder (hitsuyō-teki kyōdō soshō), requiring a unified judgment regarding the disputed interest.
  • Complexities in Articulating Claims/Defenses: Especially in scenarios under Article 50 where a defendant (the applicant) brings in the plaintiff's successor, or vice-versa, complex doctrinal discussions exist in Japanese legal scholarship regarding precisely how the successor's claims or defenses are then formulated and pursued within the existing procedural framework. For instance, questions arise as to whether the successor must independently re-assert the claim or if the original applicant's pleadings suffice, and who bears the responsibility for fully articulating the dispute involving the new party. (These detailed academic debates, such as those by scholars Nakano, Inoue, and Shindō mentioned in some commentaries, highlight the procedural intricacies that can arise).

VI. Res Judicata and Other Effects

A primary purpose of soshō hikiuke is to ensure that the judgment is effective:

  • A judgment rendered after a valid assumption of suit will have res judicata effect on the successor who was duly made a party to the litigation.
  • This enhances the finality of the dispute resolution by binding the actual current holder of the relevant substantive interest.

VII. Comparing with Third-Party Practice in Other Jurisdictions

  • U.S. FRCP Rule 14 (Third-Party Practice / Impleader): This allows a defendant to bring in a third party who is or may be liable to the defendant for all or part of the plaintiff's claim against the defendant (e.g., for indemnification or contribution). This has a different focus—derivative or secondary liability—than Japanese soshō hikiuke, which concerns compelling a successor to the primary disputed right or obligation to join.
  • U.S. FRCP Rule 25(c) (Transfer of Interest): This rule states that if an interest is transferred during an action, the action may be continued by or against the original party, unless the court, on motion, orders the transferee to be substituted in the action or joined with the original party. This is conceptually closer to Japanese litigation succession (both voluntary sanka shōkei and compelled soshō hikiuke). However, the Japanese system, with its distinct provisions for voluntary intervention by a successor (Art. 49) versus compelled assumption initiated by an existing party (Arts. 50, 51), offers a more specifically structured framework for different scenarios of succession to the res litigiosa.

VIII. Strategic Considerations

  1. For an Existing Party Whose Opponent Transfers the Disputed Interest: If you become aware that the opposing party has transferred the right or obligation you are litigating over, promptly consult with counsel about filing a motion for assumption of suit. This can be crucial to prevent your judgment from becoming a "paper tiger" against an entity that no longer holds the relevant interest.
  2. For a Successor to a Disputed Right/Obligation: Be aware that, in addition to potentially choosing to voluntarily intervene (under Art. 49 if advantageous), you might be compelled to join an ongoing lawsuit under Arts. 50 or 51. This possibility should be considered during due diligence for any transaction involving assets or obligations known to be subject to litigation.
  3. Due Diligence in Transactions: When acquiring rights or assuming obligations, especially those that are identifiable and potentially contentious, thorough due diligence should include inquiring about any pending litigation. The risk of being drawn into such litigation post-acquisition is real.

IX. Conclusion

"Assumption of litigation" (soshō hikiuke) under Articles 50 and 51 of the Japanese Code of Civil Procedure provides a vital, if specialized, tool for ensuring that lawsuits remain focused on, and judgments are binding upon, the true holders of disputed rights and obligations when these interests are transferred mid-litigation. Distinct from voluntary intervention by a successor, this mechanism empowers existing parties to proactively bring successors into the fold, thereby upholding procedural efficiency and the ultimate effectiveness of the judicial process.

While its application involves careful consideration of the nature of the succession and specific procedural requirements, soshō hikiuke plays an important role in adapting ongoing legal proceedings to substantive changes in interest ownership, reinforcing the principle that justice should be rendered between the actual stakeholders.