Tensei Shitara Slime Datta Ken (WN) - Chapter 323

This novel is also known as Long Live the Mad Wife!

Daughter of the Feng Family, born a waste. Forced to marry a fool in an attempt to expel evil influences. When the first killer from the 21st century possessed this body, the sky and the earth surged. She was indifferent and cold-hearted but she let her guard down around him alone. She thought he was a pleasant sheep but didn’t expect him to be a gray wolf in disguise!

- Description from Novelupdates

With a marriage contract forcefully done, he married her, and all she could do was comply, and resent him deeply for that and for all the following misunderstandings they faced.
However, it was already too late when she understood she actually loved him.

[R-18, Mature Element Warning!] [Multiverse!]A young man with a questionable job dies, eaten by a shark. To his surprise, afterlife was a spinning roulette that decided his next world and powers, with an annoyed Goddess supervising the process.The Gamer System welcomes him with open arms, and he shivers in the endless potential it holds. If used right, he knew The Gamer could step beyond even Godhood. Beyond God.Out of desperation, that was exactly what his goal became. The Goddess was a snitch, and now she and her fellow Gods wanted him dead. What, and why?In the end, [Soul 799], soon to be renamed as [Neji Hado], becomes a Cursed Soul.-—-Tags: Gamer-System, Gray-MC, Harem, Incest, Mature, Multiverse, R-18, OP-MC, World-Hopping.First World: My Hero AcademiaSecond World: NarutoThird World: Fate/Grand OrderFourth World: High School DxD

A replica of Marquis Kieran Vale, the son of the Marchioness of Vale, who she deemed a failure. That was all she was. No, she was now referred to as “he.” At least until she met Claude Del Ihar.