The Twins' Circumstances
Ongoing | Mada Tetsukazu | 2000 released
A brother and a sister are in love with each other but don't have the courage to confess because of their bond and their parents possible reaction; there are some misunderstandings little spoiler (it's explained in the 1 chap though) no incest They aren't actually twins nor siblings. He's the son of the parent's friend who died long ago. They AREN'T blood related.
Hinmin Choujin Kanenashi-kun