The original sprites are 720p. A modder on /vg/ created 4K upscales using ESRGAN. Search for ErogeSubete_HD.7z – extract to game\assets\pic . This fixes blurry close-ups.
Some versions require a manual crack (e.g., steam_api.dll / config.ini ): eroge de subete wa kaiketsu dekiru the install
Back this up if you reinstall Windows.