My Cousin, The Pushy Prince

Overview

Masato's cousin Yuusei used to be so cute... but now that he's all grown up, he's naughty, ridiculously handsome, and won't take no for an answer! Masato's younger cousin has just started college, and he's going to be lodging with Masato's family until he graduates. Things are already off to an awkward start when Masato accidentally witnesses Yuusei getting rejected by his little sister, Saki. What's more, Masato's frantic efforts to console his cousin are rewarded with... Yuusei running his fingers over his body! Wait. Was Masato his target all along!? He'd always thought of Yuusei as a cute little brother. How will he respond to his, er, adult advances!? (Source: Renta!)

Source: AniList