Hey,

I can't clearly remember if it was a manga or manhwa, sorry.
The story is about twins exchanging their roles, the girl is kinda boyish, she knows martial arts and she's smart. Her twins brother must join the army but she knows he's too weak so she will join instead and her brother will crossdress as his twins sister.

I think the male lead is the general.

Thank youuuuu

Samurai High School?

The Villain Discovered My Identity?

Nope it's not this one, the one I'm looking for take place during ancien time with an emperor, harem etc... but thank you !

@ Alimeru
Her coward of twins brother ran away with his lover in The Villain Discovered My Identity. In the manhwa/manga I'm looking for the brother crossdress as his sister. But thank you !

I think this is what you're looking for
Ao no Souyoku - Phantom of Dragon

It's not but thank you I will read this one, it looks good! The one I'm looking for the story was during ancient time so no airplanes

https://www.mangaupdates.com/series.html?id=13517
^The change!
Is this the one?

There's also this one where the brother I think runs away first and then later probably crossdresses as his sister to avoid situations.
Complying with Imperial Edict