Minatsu from Da Capo II. I revisit her scenes often. I probably read a lot more into her character than is there, but I think she covers some interesting ground for a robot girl. I wasn't going to play her path at first, but, like halfway through Anzu's route you have a conversation with her about robot nature and her machine soul. That conversation made me stop Anzu's route and start the game over going down Minatsu's. It's things like that which made her stick in my mind.
Sakura from the Da Capo series also sticks out in my mind, but not as a love interest. She's more interesting as an a