Satoshi starts as a 'small man' in all aspects. His dick is small, he's introverted, nonathletic, inexperienced, has a very narrow/boxed way of thinking and he's even kinda prideful with nothing to back it up. In several parts he does get better and when he does its very nice to see. He truly loves Mary and only his insecurities hold him back until other guys enter the frame.
Mary is on the other end. She's outgoing, sexy, athletic and popular. More free spirited than the box-like satoshi but still very in love with him. A girl that likes sex not only for the emotional part of it but also for the physical aspect, which ends up being what drives most of the NTR despite her claims. Somehow a lot more emotionally mature than Satoshi, she still fucks up with him sometimes.
Kento is a dick, in all senses. Biggest cock ever, cums gallons, can go for hours, better at sex than anyone else, has dating experience and has fucked who knows how many women over the years. He's very confident and assured in that aspect. He's written to be the opposite of satoshi at first glance and so he shares a few traits with Mary. He's also the biggest douche in the game, even more so than Rin's terrible boyfriend. Not because of his attitude, but because he's a prime example of the power dynamics that people and laws have been trying to avoid for years. Him interacting with others and stealing them girls feels like a teen or a young adult tutoring some children, he can give the wrong advice to whoever he wants, focus on other, give them candy or just shame them, etc.
That said, Satoshi is one of the few characters that's constantly trying, sometimes too little, too late, or in a completely wrong manner, but he does some honest tries. Mary also tries, but she steers away easily despite being the more mature between the two, sometimes she fails to meet him halfway and instead defaults to just tolerating his shortcomings.
Something all male characters in the game share is some sort of inferiority complex. The one who rides it best is Kendo, mostly due to him being the most experienced one in the cast (in several ways), while Satoshi deals with it the worst (given his inexperience and lack of a proper outlet or guidance). But the others also show it a lot, Arato is an asshole constantly trying to prove himself the biggest winner in the room or else his ego crumbles into dust, Hanako's dad is an over controlling douche, Yoshi has a cuck fetish, etc.
Great game. To be honest I only want like 3 characters to end up in happy loving relationships and those are Satoshi, Hanako, and Rin. Kinda feel like they all deserve better.