Onegai Twins follows Maiku, Karen, and Miina. Maiku is a high school boy orphaned at an early age, now living in a house he believes is the house he grew up in. His only link to his youth is a picture of his house, himself, and his twin sister. Karen and Miina are also orphaned at an early age.

Miina was adopted by a family, but she leaves her adoptive family and arrives at Maiku's doorstep with the same picture that Maiku has. Karen comes straight from an orphanage to Maiku's place with the same picture in her hand. As the two girls become emotionally closer to Maiku and Maiku starts to open up to them, the love birds realize that one of them is a sibling and their love cannot be fulfilled. Or will it?

Originally created by Please! and Story by Akikan.