Good start to write the endings, especially the Satoshi route. I think its pretty obvious that Satoshi was a quick shooter mostly because on how he felt inadequate since he knows hes on the smaller side but since he found true love he can keep going for hours and actually compete with his Alphawaifu. A very funny hentai trope would be that her vagina actually goes down so Satoshi can hit the cervix like any hentaiprotag can which makes Mary go crazy with lust about him.
Small penis worship is a thing too. Maybe focus the storywriting on the Satoshi route about how beautiful he and his dick is and that through love Mary gets the best orgasm in her life. Its clear that he looks much better compared to that one fuckface whose name I forgot based on the truth or dare swinging scene.
What I found sad about the whole thing is we don't know just how big the woman are, 3 measurements and all and how big the men are. Is Satoshis pp 3.5 inches? 4? 5? Whats Marys cup size? Is Kendo 13 inches? More data for this stuff is always important. The japanese again are miles ahead since at least they flesh out the characters but you don't see any of this here. In a game all about bodyworship theres not much stuff to work with there. The images mostly carry the plot but leave out most of the fun. In most japanese and asian games its both. They have decent and detailed writing and data so the reader has a better mental image. I'd say learn from them. They do a much better job than me explaining this shit
Any of this doesn't really matter as long as its conveyed that ones love for someone goes deeper then even the deepest depths of any vagina, makes me really happy that the writer of this game understands this as well. Godspeed dev