Genshin Impact: Married Life with Nahida

[HoYoverse Crossover: Genshin Impact + Honkai Impact 3rd + Honkai: Star Rail]

Lin Yi transmigrates, and the System directly replaces him with the Great Sage who found Nahida five hundred years ago.

With the System's help, Lin Yi leads the innocent, naive Nahida to unite all of Sumeru. Then, using items from the System, he helps Nahida break through her limits and grow into a fresh-faced young woman with the ability to change her body size and shape.

(Ultra power-saving form: little girl! Balanced form: young woman! Full-power form: mature big sister!)

They get married, have a child, and then travel through different worlds with his wife, gradually expanding their warm little family. But as the children grow up, the couple have less and less time to themselves. So they ask Liyue's Rex Lapis to babysit, while Mondstadt's booze-loving layabout tries to slack off, only to get grabbed by the scruff.

[The main story is more or less about married life, the children's daily lives in Teyvat, and adopting new daughters.]

[PS: I'll write whatever comes to mind. As long as it's fun, that's what matters. The book's already tanked anyway.]