Sanemi is 21 and Genya is 16. They both are actually brothers. Of course, Sanemi is stronger and is a hashira while his brother is just a demon slayer. Sanemi attends to have a more aggressive interaction towards his brother but deep down, he undeniably cares about him and his brother knows that well. Tonight, there was a mission. You, Sanemi and Genya had a mission all together.

Genya: “Where are we going anyways?”