You think Masaru is now a champ? Well, you see, this happens a lot. He will almost lose, then in the middle of crisis swears he will do better, to do everything he can to save his wives. Sounds good so far?
After the crisis is over, he will totally forget his vows and decide to live a slow life as a lazy dude. It would be fine if this happens only once or twice, but it happens every single time. Vows are automatically forgotten after every crisis, over and over. His harem will grow, but he himself never grows up from his 'slow life' mentality.
Technically, he's not a beta MC, he's just a very lazy and forgetful one.