In Japan, as in many jurisdictions, a significant number of civil disputes are resolved not by a full trial and judgment, but through agreements reached by the parties with the involvement of the court. These can take the form of an "in-court settlement" (訴訟上の和解 - soshōjō no wakai) reached during ongoing litigation, or a "mediated agreement" (調停に合意する - chōtei ni gōi suru) achieved through formal civil mediation proceedings (民事調停 - minji chōtei). A crucial feature of these court-facilitated agreements is that, once properly recorded, they generally possess the same legal effect and enforceability as a final and binding court judgment[cite: 82, 86].

But what happens if a party subsequently believes that the settlement or mediation agreement itself was fundamentally flawed—for instance, induced by fraud or mistake, or concluded without proper authority? Challenging such an agreement involves navigating specific procedural pathways, each with its own implications for court fees, which are determined by the "value of suit" (訴額 - so'gaku).

The Powerful Effect of Court Settlements and Mediations

Under Japanese law, an in-court settlement recorded in the court protocol (和解調書 - wakai chōsho) has the same validity and effect as a final and binding judgment (Code of Civil Procedure [CCP], Art. 267)[cite: 83, 84]. Similarly, an agreement reached in civil mediation and recorded in a mediation protocol (調停調書 - chōtei chōsho) is also afforded the same status (Civil Mediation Act, Art. 16)[cite: 86]. This means these agreements are not mere private contracts; they become enforceable titles (債務名義 - saimu meigi) upon which compulsory execution can be based.

The legal nature of an in-court settlement is often described as having a dual character: it is both a substantive contract between the parties resolving their dispute through mutual concessions (as per Civil Code, Art. 695 [cite: 82]) and a procedural act terminating the lawsuit[cite: 82]. Prevailing case law in Japan appears to support theories reflecting this dual nature[cite: 82].

Grounds for Challenging a Court Settlement or Mediation

Despite their judgment-like effect, court settlements and mediated agreements are still based on the consent of the parties. If this consent is vitiated, or if other fundamental defects exist, the agreement may be challenged. Grounds for challenge can include:

• Substantive Law Defects:
  • Mistake concerning a fundamental basis of the settlement (e.g., a shared erroneous assumption)[cite: 83].
  • Fraud or duress inducing one party to agree[cite: 83].
  • Content that violates mandatory provisions of law or public policy[cite: 83].
  • Lack of legal capacity of a party at the time of agreement.
• Procedural Defects:
  • Absence of a properly prepared and recorded court protocol detailing the agreement (though this is rare in practice)[cite: 83].
  • Lack of authority of a representative who purported to agree on behalf of a party.

Procedural Routes for Challenging Validity

The Japanese Code of Civil Procedure does not contain an explicit, dedicated procedure for challenging the validity of an in-court settlement or mediation after it has been recorded. This has led to considerable legal debate and the emergence of several potential procedural avenues[cite: 83]:

1. Motion to Set a New Court Date in the Original Proceeding (期日指定申立て - kijitsu shitei mōshitate):
   One theory suggests that the party challenging the settlement should apply to the very same court where the settlement was reached, requesting that new court dates be set to re-examine the validity of the settlement and, if it's found invalid, to resume the original litigation[cite: 83]. The advantage of this route is its potential efficiency, as the court would already be familiar with the case and could utilize existing case materials[cite: 83].
2. Filing a New Lawsuit (新訴提起 - shinso teiki):
   This is often the more commonly accepted route in practice, particularly when the original lawsuit has been definitively terminated by the settlement.
   • Suit for a Declaration of Invalidity (和解無効確認訴訟 / 調停無効確認訴訟 - wakai/chōtei mukō kakunin soshō): A party can file a new, independent lawsuit seeking a declaratory judgment from the court that the settlement or mediation agreement is null and void[cite: 83, 86]. Japanese case law generally permits such actions.
   • Claim Objection Suit (請求異議訴訟 - seikyū igi soshō): If the settlement or mediation protocol is being used by the other party as an enforceable title to levy execution, the party challenging its validity can file a "claim objection suit"[cite: 83]. This type of lawsuit seeks a judgment declaring that execution based on that specific title is impermissible due to the invalidity of the underlying settlement or mediation. The Supreme Court of Japan has affirmed the permissibility of this route for challenging court settlements that function as enforceable titles, partly because such settlements, while having the effect of a judgment, may not carry the full scope of res judicata that would bar all challenges to their formation (Judgment of the Supreme Court, February 15, 1968, Minshū Vol. 22, No. 2, p. 184)[cite: 86].
3. Concurrent Use Theory (競合説 - kyōgōsetsu):
   Some theories suggest that various methods of challenge might be concurrently available, leaving the choice to the challenging party. However, this is often criticized because the procedural position of the party defending the settlement's validity can differ significantly depending on the route chosen, and giving unfettered choice to the challenger may be unfair[cite: 83].

While the "motion for new court date" offers procedural economy, the ability to file a new suit for a declaration of invalidity, ensuring a full three-instance review if necessary, is also a significant consideration.

Court Fee ("So'gaku") Implications for Challenges

The method chosen to challenge a settlement or mediation, and the nature of the original dispute, will influence the calculation of the "value of suit" (so'gaku) for court fee purposes.

(Note on fees for the original settlement itself: If an in-court settlement includes matters that were outside the scope of the original lawsuit's object, this does not typically lead to an increase in the so'gaku or additional fees for the original suit that was settled[cite: 84]. The author of the source text notes this contrasts with practices in some other jurisdictions like Germany and with how scope expansion is treated in Japanese civil mediation, suggesting a potential imbalance[cite: 84].)

A. Fees for a Motion to Set a New Court Date (Kijitsu Shitei Mōshitate)

• The Motion Itself: Prevailing practice has often been that no specific court fee is required for filing the mere motion to set a new court date to challenge the settlement's validity[cite: 84].
• If the Settlement is Found Invalid and the Original Suit Reopened (Author's View from source text):
  The author of the source text argues that if the court agrees the settlement is invalid and decides to resume the original litigation, this is a substantive development, not just a simple rescheduling. In such a case:
  • The "value of suit" for the reopened proceedings should logically be the so'gaku of the original lawsuit that was purportedly terminated by the now-invalidated settlement[cite: 84]. The author debates whether this should be the full original so'gaku or perhaps half (by analogy to reopening a default judgment), but leans towards the full original so'gaku due to the principle that a court settlement has the same effect as a final judgment (CCP Art. 267)[cite: 84].
  • Matters that were included in the settlement but were outside the object of the original lawsuit should not be added to the so'gaku for these reopened proceedings[cite: 84].
  • The author also refutes the idea that the so'gaku for the reopened proceedings should simply be the monetary amount agreed in the (now invalidated) settlement, as it is the original claim that is being revived and re-litigated[cite: 84].

B. Fees for a New Lawsuit Declaring Invalidity (Wakai/Chōtei Mukō Kakunin Soshō)

When a new lawsuit is filed to declare a settlement or mediation invalid:

• The so'gaku is the economic benefit the plaintiff (the party challenging the settlement) gains from the declaration of invalidity[cite: 86].
• According to prevailing academic views, this benefit is typically based on the value of the claim, right, or legal obligation that was recorded in the challenged settlement or mediation protocol[cite: 86].
  • Example from the source text: A ¥5 million loan dispute was settled with Debtor Y agreeing to pay Creditor X ¥3 million, and X waiving the remaining ¥2 million[cite: 86].
    • If Debtor Y sues to declare the settlement invalid, their benefit is avoiding the ¥3 million payment obligation. Thus, the so'gaku = ¥3 million[cite: 86].
    • If Creditor X sues to declare the settlement invalid (perhaps to pursue the full original amount), their benefit is the potential revival of the ¥2 million portion they waived. Thus, the so'gaku = ¥2 million[cite: 86].
    • If the settlement involved a non-monetary obligation like eviction from property, the so'gaku would be analogous to a standard lawsuit for eviction (e.g., based on the property's value or relevant leasehold interest)[cite: 86].
• If the defendant in this invalidity suit files a preparatory counterclaim to re-assert their claim from the original, settled lawsuit (conditional on the settlement being found invalid), the so'gaku for this counterclaim would be that of the original claim. However, for fee purposes, it would likely be seen as economically unitary with the invalidity suit, meaning the "difference principle" for counterclaim fees would apply (the fee for the counterclaim would be its standalone fee minus the fee for the invalidity suit)[cite: 86].

C. Fees for a Claim Objection Suit (Seikyū Igi Soshō) Based on Invalidity

If a party files a claim objection suit arguing that an enforceable settlement or mediation protocol is invalid:

• The so'gaku is the value of the claim as stated in the enforceable title (the settlement or mediation protocol) whose execution is being challenged[cite: 86].

Special Cases: Pre-Litigation Settlements and Civil Mediations

• Pre-Litigation Settlements (起訴前の和解 - Kiso-mae no Wakai) (CCP Art. 275):
  Parties can apply to a Summary Court for a settlement procedure before any formal lawsuit is filed[cite: 86]. If successful, the recorded agreement has the same effect as an in-court settlement[cite: 86].
  • Initial Application Fee: The fee for initiating this pre-litigation settlement procedure is a fixed nominal sum (¥2,000 as per the Civil Procedure Costs Act, Appended Table 1, Item 9)[cite: 86].
  • Challenging via Suit for Declaration of Invalidity: If this pre-litigation settlement is later challenged through a separate lawsuit seeking a declaration of its invalidity, the so'gaku for that new suit is the value of the claim recorded in the pre-litigation settlement protocol[cite: 86].
• Civil Mediations (民事調停 - Minji Chōtei):
  Agreements reached in formal civil mediation proceedings and recorded in a mediation protocol also have the same effect as a court settlement (Civil Mediation Act, Art. 16)[cite: 86].
  • Suit for Declaration of Mediation Invalidity (調停無効確認の訴え - Chōtei Mukō Kakunin no Uttae): The plaintiff's benefit is being relieved of the obligations under the mediation. The so'gaku is therefore the value of the claim(s) recorded in the mediation protocol[cite: 86].
  • Joinder with Claim Objection Suit: If a suit to declare a mediation invalid is joined with a claim objection suit (where the mediation protocol is the enforceable title being challenged), these are considered economically unitary. The so'gaku is the value of the claim in the mediation protocol, and no fee aggregation occurs[cite: 86].

Conclusion

Challenging the validity of court settlements or mediated agreements in Japan, which carry the weight of final judgments, requires careful consideration of the available procedural avenues. Whether opting for a motion to reopen the original case or initiating a new lawsuit (for a declaration of invalidity or a claim objection), the "value of suit" for court fee purposes is generally tied to the economic substance of the rights and obligations established by the challenged agreement. For parties believing a settlement was fundamentally flawed, understanding these valuation principles is a key step in assessing the viability and cost of seeking redress.