From Today, It's My Turn!!: Sagawa The Hero & Those Two summary:

It's been 25 years since Mitsuhashi and Itou suddenly disappeared right before the high school graduation ceremony. Sagawa, now in his forties, is working at a dead end job after giving up on his dreams. When he finds out that his coworker Miyabi is being abused by her older brother, he tries to intervene, thinking that he could be like those two were back in the day. However, it backfires horribly, and he finds himself on the verge of being killed. All out of options, he prays for help in desperation, when Mitsuhashi and Itou suddenly appear out of nowhere, looking exactly like they did all those years ago!