 If you liked
Onegai☆Twins
|
 ...then you might like
Boku wa Imouto ni Koi wo Suru
|
Forbidden love is one of those genres in the anime world that's explored in both series.
In both series, there is a forbidden romance between the main characters. Although Onegai Twins focuses more on a love triangle, both series contains rivals and drama.
Both series also has comedy although Boku wa Imouto ni Koi wo Suru focuses more on the drama side. Additionally, both anime(s) have that mature and emotional side where the main character struggles to find his way throughout the story.