Manga How a Realist Hero Rebuilt the Kingdom / Genjitsu Shugi Yuusha no Oukoku Saikenki

Kazuya Souma’s grandfather left him with the request that Kazuya starts his own family and protect it with everything he has. Kazuya swears to uphold that wish -- until he’s summoned to another world as a hero!

In this world, the countries are being ravaged by the demon world, with monsters pouring out and attacking the land. Various war efforts and an increase in refugees have sent the kingdom into disarray -- but Kazuya manages to keep calm and propose solutions to the situation with the king. From this demonstration in skill, the king decides to hand his throne to Kazuya, and have him marry his daughter! This is Kazuya’s story in trying to restore a kingdom from another world!