紅戦記　～くノ一忍び愛～

Main character is a genius programmer who gets to know from his dying grandfather that their lineage is protected by Shinobu ninja. Moreover, his sweetheart and childhood friend Mizuho turns out to be his bodyguard. Protagonist is anxious to invite the beauty president of the rival company for a dinner, but Mizuho fiercely blocks the attempt. What secrets still remain hidden?

[From vndbreview]