He's in Love with Him.

Mochida, a new employee at Kiryu Tax Accounting Office, secretly admires his boss, Kiryu. One night on a train, Mochida witnessed Kiryu gently helping a woman who was being harassed by a drunk. Mochida had wanted to step in himself but couldn’t move, and that helplessness left a lingering sense of guilt. Kiryu, always quick to notice Mochida holding back his words, offers subtle support and a helping hand every time. With each of those moments, Toa finds himself falling for him more and more...!

(Source: Taiyoh Tosho, translated)