Moto Sekai Ichi'i no Sub-chara Ikusei Nikki - Chapter 10: Reus Dungeon

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.

In Academy City, magic and science coexist in an unwavering power struggle. Toma Kamijo, an academically-challenged student in Academy City, wields the power of the Imagine Breaker in his right hand, which allows him to completely negate all supernatural powers – as well as his own luck. When he happens upon a mysterious nun named Index, whose mind has been implanted with the Index Librorum Prohibitorum – 103,000 ancient texts banned by the Church – Toma’s luck is about to be pushed to its limits when he finds himself in the middle of a war he never expected!