Burden of Proof for Copyright Similarity in Japan: What Must Plaintiffs and Defendants Demonstrate?

In Japanese copyright infringement litigation, establishing "similarity" between the plaintiff's copyrighted work and the defendant's allegedly infringing work is a cornerstone of the plaintiff's case. While the ultimate judicial standard involves assessing whether one can "directly perceive the essential expressive features" of the original work within the later one, the procedural question of who needs to prove what—the allocation of the burden of proof—is critical to the practical conduct and outcome of such disputes.

The Plaintiff's General Burden to Establish Infringement

As in most civil litigation, the plaintiff (the copyright holder) generally bears the overall burden of proving the constituent elements of copyright infringement. This typically includes demonstrating:

1. Ownership of a valid copyright in a specific work.
2. The act of copying by the defendant, which itself has two components:
   • Access by the defendant to the plaintiff's copyrighted work (or a presumption of access if the works are strikingly similar and the plaintiff's work was widely disseminated).
   • Sufficient similarity between the defendant's work and the plaintiff's copyrighted work.
3. That the defendant's unauthorized activity (e.g., reproduction, adaptation, public transmission) falls within the scope of one or more of the exclusive rights granted to the copyright holder under the Japanese Copyright Act.

The element of "similarity" is thus a key hurdle that the plaintiff must clear.

The Plaintiff's Initial Task: Demonstrating Similarity in Creative Expression

To satisfy their burden regarding similarity, the plaintiff must demonstrate to the court that the defendant's work is indeed similar to their copyrighted work in terms of its creative expression. This is not merely about showing superficial resemblances but about establishing a commonality in those aspects of the plaintiff's work that are original and protected by copyright.

In practice, this involves:

• Clearly identifying the copyrighted work and the allegedly infringing work.
• Presenting both works to the court, often through side-by-side comparisons.
• Specifically pointing out the shared expressive features that the plaintiff alleges have been illicitly taken. These are the features that the plaintiff contends constitute the "essential expressive features" that are "directly perceivable" in the defendant's work.

The plaintiff must effectively show that the defendant’s work is not just inspired by the same general idea but has reproduced a substantial part of the plaintiff's unique, creative way of expressing that idea.

The Defendant's Rebuttal: Challenging Protectability and Highlighting Differences

Once the plaintiff has presented a prima facie case for similarity, the defendant will typically mount a defense aimed at rebutting this claim. While the ultimate burden of persuasion for similarity remains with the plaintiff, the defendant has a crucial role in producing evidence and arguments to counter the plaintiff's assertions. Common defense strategies directly addressing the similarity (or lack thereof) include:

1. Arguing that Shared Elements Are Not Protectable: This is a cornerstone of many defenses. The defendant will seek to demonstrate that the elements common to both works are not, in fact, creative expression protected by copyright. This involves arguing that the shared features fall into categories such as:
   • Abstract Ideas: The similarity exists only at the level of an unprotectable idea, theme, or concept.
   • Facts or Common Knowledge: The shared elements are factual information, historical data, or widely known public domain elements.
   • Commonplace Expressions (arifureta hyōgen): The expressions used are ordinary, standard, trivial, or so conventional within a particular genre or for a specific subject matter that anyone creating a similar work would likely use them. Such expressions are deemed to lack the necessary authorial individuality for protection.
   • Elements Dictated by Function or Scenes à Faire: The shared features are dictated by technical or functional requirements, or are standard or indispensable elements in the treatment of a given topic (similar to the scenes à faire doctrine in U.S. law).
2. Highlighting Dissimilarities: The defendant will also emphasize the differences between their work and the plaintiff's work. The argument here is that even if some superficial resemblances exist, the works are, on the whole, substantially different, and therefore, the essential expressive features of the plaintiff's work are not directly perceivable in the defendant's creation.

The Critical Role of Evidence in Proving "Commonplaceness"

A particularly vital strategy for defendants is to assert that the plaintiff's work itself, or at least the parts allegedly copied, possesses low creativity or consists of commonplace expressions. If this is established, the scope of copyright protection for the plaintiff's work becomes very "thin," meaning only near-identical copying would constitute infringement.

To substantiate a claim that certain expressions are "commonplace," a defendant often needs to present concrete evidence to the court. This might include:

• Examples of prior existing works (predating the plaintiff's work) that use similar expressions.
• Evidence of widespread use of such expressions in the relevant industry or artistic field.
• Expert testimony regarding standard practices or common motifs within a genre.

Japanese courts do consider such evidence. For instance, in cases involving relatively simple designs or motifs, such as the Fuwafuwa Shiki no Tayori case (Tokyo District Court, October 30, 2014) which concerned small seal designs, the defendant’s submission of numerous pre-existing similar designs ("comparison designs") was crucial. The court referred to these comparison designs to determine that many features of the plaintiff's seal designs were, in fact, "commonplace expressions" for the depicted subjects (e.g., a lotus flower, a gourd). This led to a finding of low creativity for most of the plaintiff's designs and, consequently, a denial of similarity for most of the defendant’s allegedly infringing seals, as they were not virtually identical. Similarly, in the Urusee Tori case (Tokyo District Court, October 14, 2020), concerning character illustrations, the defendant successfully argued that many of the plaintiff character's features were commonplace by presenting various other existing characters with similar traits.

This demonstrates that the defendant’s effort in gathering and presenting evidence of commonplaceness can be pivotal in narrowing the perceived scope of the plaintiff's copyright and thereby defeating a claim of similarity.

Judicial Handling of Varying Evidentiary Levels

The level of evidence presented by both parties significantly influences the court's decision-making process:

• Robust Evidence from Both Sides: When both the plaintiff and defendant provide detailed arguments and substantial evidence regarding the creative elements, the commonality (or lack thereof) of expressions, and the existence of prior art or commonplace forms, the court is well-positioned to make a thorough and well-grounded assessment of similarity.
• Insufficient Evidence: A more challenging situation arises when evidence is sparse, particularly in smaller disputes where parties might have limited resources for extensive research or expert testimony.
  • If a defendant merely asserts that an expression is "commonplace" without providing supporting evidence, the court might have to rely on its own general knowledge or judicial notice. For expressions that are obviously generic in a widely understood field, this might suffice.
  • However, for more specialized or less obviously generic expressions, the absence of concrete evidence from the defendant proving commonplaceness could lead the court to give greater weight to the plaintiff's claim of creativity for those shared elements. In such a scenario, a finding of infringement might occur where it could potentially have been avoided if the defendant had more effectively demonstrated the lack of protectable originality in the shared features. This underscores that the practical outcome can indeed be influenced by the diligence of the parties in substantiating their claims about the nature of the expressions at issue.

The Nature of the Similarity Finding: Legal Evaluation Based on Facts

Under Japanese civil procedure, the ultimate determination of whether actionable "similarity" exists—i.e., whether the "essential expressive features" of the plaintiff's work are "directly perceivable" in the defendant's work—is considered a legal evaluation (法的評価 - hōteki hyōka) made by the court, rather than a pure finding of objective fact.

However, this legal evaluation is not made in a vacuum. It must be grounded in underlying factual determinations. In terms of burden of proof for these underlying elements:

• The plaintiff bears the burden of establishing the "evaluation-basis facts" (評価根拠事実 - hyōka konkyo jijitsu)—that is, presenting the specific features of their copyrighted work and the corresponding features in the defendant's work that they contend support a finding of similarity in creative expression.
• The defendant, in turn, bears the burden of establishing "evaluation-hindrance facts" (評価障害事実 - hyōka shōgai jijitsu)—that is, proving facts that would negate or undermine the plaintiff's asserted basis for similarity. This includes, crucially, facts demonstrating the commonplaceness of the allegedly copied features, the existence of significant differences that alter the expressive character, or that the shared elements are unprotectable ideas.

For visually ascertainable works like illustrations or photographs, the presentation of the works themselves as exhibits might often suffice for the plaintiff to assert the relevant "evaluation-basis facts" concerning their expressive features. For more complex or lengthy works, such as literary texts or musical compositions, the plaintiff would need to more specifically pinpoint the passages or sections where similarity in creative expression is alleged.

Conclusion: A Dynamic Interplay of Burdens

While the plaintiff in a Japanese copyright infringement case carries the initial and ultimate burden of persuading the court that the defendant's work is actionably similar to their own creative expression, the process is a dynamic one. The defendant has a significant opportunity and, practically speaking, often a necessity, to actively rebut the plaintiff's assertions. A key element of this rebuttal frequently involves challenging the protectability of the shared elements by demonstrating their lack of creativity—for instance, by proving that they are commonplace within the relevant field.

The depth and quality of evidence provided by both sides regarding the originality or commonplaceness of the disputed expressive features can substantially influence the court's legal evaluation of similarity. In situations where such evidence is limited, the court's decision may rely more heavily on its own assessment of the inherent nature of the expressions or default presumptions. Therefore, a thorough understanding of these burdens of proof and the evidentiary requirements for substantiating claims about creativity and commonplaceness is indispensable for effectively litigating copyright similarity in Japan.