This is a well-made shoot 'em up game with the hentai being an afterthought. The small amount of hentai content is confined to the holding cells you can visit between missions. And even then, they're still scenes that rely on the accompanying erotic text. You can play through the entire game without seeing any h-content.

Official Website: http://purpleheart.jp/game07/

DLsite Link: http://www.dlsite.com/maniax/work/=/product_id/RJ052823.html