In a crossover anime, the only way to become stronger is by marrying a wife.

[Seeking virtuous wives!]
[Requirements: Under 30, attractive, and with a gentle personality preferred.]
[Includes a large number of experience cards, class cards, skill cards, and weapons!]
[Sign a destiny contract now and receive it instantly!]
[My energy is limited, first come, first served!]
He transmigrates into various anime worlds, unlocking a new realm teeming with monsters. Meanwhile, Tsukikawa Shuu, who had been contemplating giving up, suddenly discovers his cheat ability is to marry and have children.
"I, Tsukikawa Shu, abhor the rampant impotent male protagonists and resolutely reject the despicable practice of 'Why flirt if you won't marry me!'"
……
Goto Ichiri: "Eh? I got married? Well, that makes sense, I'm not good at saying no to people..."
Kitagawa Kaimu: "Marriage? Haha, sure... Wait! Are you serious?!"
Fujiwara Chika: "It's unavoidable, but we shouldn't let the student council find out about our relationship..."
Yukino Yukinoshita: "You can marry me, but could you please take down that 'seeking virtuous wives' advertisement first?"
(Oregairu, Lonely Rock, Don't Be My Older Brother, Dress-Up Doll)