Temperature Rising(2003)

Kimi no Ondo

Mizumo had a rough childhood ― he grew up with no parents and came from a broken home. When his long-time childhood friend, Minori, finds out that he's been having sex for money with teachers at school, he volunteers himself to become Mizumo's "customer." At first, they told themselves that this is nothing more than a casual rendezvous for money ― but it's turning out to be little more than that!

(Source: Juné)