Sierra to Juliet

When monsters show up, espers rise as heroes. But to Doyeong, they're nothing but glorified weapons. However, when Doyeong is dragged into the United Esper-Guide Force Command, he is declared the perfect guide for the two most powerful espers alive: brothers Kangjoon and Yijoon. Thrust into a love triangle shaped by power and survival, Doyeong has to choose who and what he's willing to endure.

(Source: Tappytoon)