I'm always a fan of strip games, and yakyuken is a rare one. Its rare for strip games to remember the stripping goes both ways.
That being said, while the art isn't bad and the music isn't bad either, there isn't a lot to really justify playing against the same waifu multiple times, beyond that it is required to unlock others.
What I mean here is that, while undressing them is all fine and good, there isn't anything to really make it so you want to do it again inherently. You've already seen them naked, after all. The dialogue also is always the same, so you can't even try to justify it for seeing a potentially different outcome.
While I can get doing it to make the game longer, it just feels too artificial. While not a yakyuken game, to take a page from Strip Poker Night at the Inventory, there's a big reason to keep playing against the same opponents beyond liking them. There's variation in dialogue, and seeing special outcomes with other characters involved and the like. A yakyuken game example I can think of is PrinceBuffoon's text-based one, which kind of kept a reason to replay by giving a variation in dialogue, forfeits to offer, and stuff like that.
I think for this game to really justify itself to make you play the same waifu multiple times to unlock others, it needs something to make replaying them again worth it. Either new art or new dialogue, for example. Otherwise, it'd be better to just have all the waifus unlocked at once or unlock after beating the prior one.