This is likely a unique hash or internal code used by the distributor to manage their database and link files to specific game titles.
You cannot open "part03" by itself. You must download every accompanying part (e.g., part01, part02) and keep them in the same folder. otomi-games.com_ETGJX2RQ.part03.rar
This is the third part of a split WinRAR archive. Because visual novels and games can be several gigabytes in size, distributors often split them into smaller pieces (parts 01, 02, 03, etc.) for easier uploading and downloading. Important Usage Requirements This is likely a unique hash or internal