There is a partial design protection system in Japan to protect characteristic parts of a design. This kind of protection is applicable for any design in any field.  This protection is available for not only product designs but also building designs, graphic image designs, sets-of-products design, and interior designs.

1. How to prepare a design application

• The statement in the column “Article to the Design” should be the name of the entire product.
  (Appropriate example: “Camera”; Inappropriate example: “Part of a Camera”)
• In the column “Description of the Design”, a statement of how the part for which the design registration is requested (the claimed part of the design) is specified is necessary.
  (Example: The part represented by solid lines is the part for which the design registration is requested.)
• In the column “Description of Article to the Design”, applicants can state the usages and functions of the claimed part of the design. Such statements about the usage and function can be given in order to help the Examiner understand the design.

2. How to prepare drawings

• The claimed part of the design should be drawn with solid lines, and any other parts should be drawn with broken lines.
  
  Source: https://www.jpo.go.jp/e/system/laws/rule/guideline/design/document/h23_zumen_guideline/05.pdf

• Alternatively, it is possible to specify the claimed part of the design by distinguishing the claimed part of the design from any other parts by coloring.
  
  Source: https://www.jpo.go.jp/e/system/laws/rule/guideline/design/document/h23_zumen_guideline/05.pdf

• The boundary between the claimed part of the design and any other parts, can be represented by dash-dotted lines.
  
  Source: https://www.jpo.go.jp/e/system/laws/rule/guideline/design/document/h23_zumen_guideline/05.pdf

• Omission of drawings that do not show the claimed portion is allowed only if the omission does not prevent the identification of the applied-for design.
• When submitting drawings including both solid and broken lines, it may sometimes be difficult to tell at a glance where the claimed portions are therein. In such cases, an additional reference drawing, in which either claimed or unclaimed portions are colored, may be added to clarify the claimed portions.

3. Important notes

• In principle, if a partial design application contains two or more physically separate claimed parts, then the application does not satisfy unity of design. However, if the design falls under any of the following, the examiner will consider subject matter that includes two or more physically separate claimed parts as one design.
  (1) Where there is unity in shape
  (2) Where there is unity in function
• A right of priority under the Paris Convention will not be recognized if the scope of the claimed part of the design filed in Japan is not identical to that in the first application from the first country.
• Amendments to change the scope of the claimed part of the design are not acceptable since such amendments are considered as change of the gist of the design which is prohibited under the Design Act.

Please also refer to the following link.
JPO Guidebook for Overseas Users: https://www.jpo.go.jp/resources/report/sonota-info/document/panhu/design_right_injapan.pdf (JPO website)