The .rar extension indicates a compressed file created by WinRAR. When a file is named with "," it means the total game data has been split.
You can use software like 7-Zip or WinRAR to extract the contents. Right-clicking "part1" and selecting "Extract Here" usually automatically pulls the data from all subsequent parts to recreate the original game folder. Media Legacy Imouto.Paradise.2.part1.rar
Serialized in Tech Gian magazine and later published as a standalone volume. Imouto.Paradise.2.part1.rar
Originally released for Windows PCs, it was later localized into English by MangaGamer in 2017. Understanding the RAR File Format Imouto.Paradise.2.part1.rar