Urenokori no Dorei Elf wo Hirotta node, Musume ni Suru Koto ni Shita

Weiss, witnesses an elf girl being sold into slavery. When he realizes that the girl is not just any elf, but a rare High Elf, he decides to buy her and raise her like a daughter.

Weiss finds himself raising a child for the first time. Thanks to his efforts, the girl, who was abused and unable to speak, regains her health. He decides to name her "Lily," after the first word she spoke.

Weiss, suddenly a parental figure, now has a new goal, to get Lily into the magic academy!

(Source: Dengeki Bunko, translated)