I Only Have Six Months to Live, So I’m Gonna Break the Curse with Light Magic or Die Trying (Manga): Volume 2 by Genkotsu Kumano

Callus continues his magical training, but he also wants to get stronger physically. While seeking help from his brother Damien, the young prince meets the sword master Sieg Lamiared and his daughter Crys. This fierce but kind girl agrees to train Callus in exchange for him teaching her magic, and the two quickly become close friends. But when a wyvern causes trouble in the surrounding forest, Crys goes missing! Now it’s up to Callus, the boy who survived thanks to the love of everyone around him, to step up and protect someone else!