The big sister who at 2rd year or maybe 3rd year high schools seems love her big brother in romance way

His little brother was at 1st year high school i guess, kinda plain looking and reject his sister advance towards him

I remember the scene at chapters around 30 ++, where the sister suddenly befriend this guy which makes the brother surpised. The brother somewhat feels weird seeing his sister like that, and i think the sister then got kidnapped, and the brother try to rescue her.

In the end the sister just pretended to make the brother jealous, she then with some weirds friend that suddenly come to the rescue, beat out the shit of the kidnapper who hire thugs here and there.

In the end the sister was happy that his brother seems care and jealous on her and call him tsundere

anyway even though this was seems looks incest, there's no sexual in physical way(even though there's some sexual joke). And this manga was a comedy gag manga , like Ane Log. So nothing serious plot here.