Mashou no Otome no Yakumawari

She got rescued from drowning by a stunning young lady, only to find that her savior's younger than her… by a LOT.

Kasumi Hana travels to meet her deceased older brother’s penpal, Urushizawa Lily, with the aim to inform her of his passing. As well as the intent to kill her, if Urushizawa had only been using him. But when they meet, instead Hana finds a woman who truly loved her late brother, and who has lost her eyesight. For Lily’s sake, she resolves to take her brother’s place.

Kairan Girls' Academy. A boarding school rich with history and tradition, attended only by orphans. It has a special system in which students are given "roles" that align with their individual goals. Hanako Shimura, a kind-hearted girl filled with dreams and expectations, enrolls into the academy hoping to make friends with everyone at school. But will she be able to?