What's the name of the manga with a girl who has two bodyguards?
Brother bodyguards sleeping in the same bed as a princess ?

It really sounds like Time Stranger Kyoko (Arina Tanemura) to me




Princess Kyoko shares her bed with two brothers guards


   

She has a time base power
It's about people having power like time, flower, dragon
there are some demons too


   she even actually has demon ears...

the brothers are orphans
She has been kissed by one of the brother but thought it was the other one,


   then some revelations made the one who kissed her appart from them (so sad moment for them)

She attends to high school, but not in our modern world, it is a mix-up between ancient/modern/fantasy/sf world
BUT she doesn't use a katana but a talking staff


It's a bright, fun and adorable manga in my opinion