I assume you already own the Japanese version. If not, you can ignore this reply. I had the same issue myself.

Even if you live in Japan, the Gamesplanet version of RE2 (the ROW / overseas version) can be activated on Steam without any problems.
However, if you already own the Japanese version (the D version), Steam will prioritize that version because both editions share the same AppID (883710).

■ Why this happens
Since both versions use the same AppID (883710), Steam automatically prioritizes the version already associated with your account region. If the Japanese version is already on your account, Steam will launch that version instead of the ROW version.

■ How to install the ROW version

1. Open Steam
2. Go to Help → Steam Support → BIOHAZARD RE:2
3. Select “I want to permanently remove this product from my account”
4. Remove the Japanese version (the one without “ROW” in the title)
5. Uninstall RE2 from your Steam Library
6. Delete the remaining folder: Steam\steamapps\common\RESIDENT EVIL 2
7. Reinstall the game — the ROW version should now install correctly

■ Notes
Save data is stored separately (usually on your C: drive), so it will not be affected.

Once the Japanese version is removed, you will not be able to use it again unless you repurchase it.

Both versions can exist on the same Steam account, but you cannot freely choose between them — Steam will automatically prioritize the version tied to your region/account status.

The “Remove from account” option is an official Steam feature and is generally safe to use.