Shinu Ummei Ni Aru Akuyaku Reijo No Ani Ni Tensei Shitanode, Imoto Wo Sodatete Mirai Wo Kaetai to Omoimasu Sekai Saikyo Ha Oredakedo, Sekai Saikawa Ha Imoto Ni Chigainai 1 (OVERLAP) [Light Novel]

[Machine Translation] Zechs, a Japanese who has been reincarnated as a countess in an RPG romance game, laments the future of his young sister Karon. Kalon, a villainous daughter, falls to the temptation of the Demon King and is sure to die in every route. -Such an adorable little sister will die an untimely death. There is no way I can allow that to happen! In order to change her fate, Zechs decides to raise Kalon correctly. Zechs, who had an aptitude for unattributed magic and was despised as incompetent, uses his knowledge from his previous life to develop new formulas one after another in order to protect Kalon! He gains uncommon power and teaches Kalon how to use magic correctly. He also detects a spy from the royal court who is after Kalon, prevents Kalon from falling into the darkness by loving him, and dispels any concerns he may have...! If I could be of help to you, my brother, I would love to be of service to you! I'm so cute, my little sister is so cute! The world's most powerful brother loves the cutest little sister! The world's strongest brother tries to avert the ruin of the most lovely sister in this heartwarming fantasy!

RPG系恋愛ゲームの伯爵令息に転生した日本人のゼクスは、幼き妹カロンの未来を嘆いていた。悪役令嬢であるカロンは魔王の誘惑に堕ち、すべてのルートで必ず死ぬ。―こんなに可愛らしい妹が非業の死を遂げる。そんなこと許せるわけがない!運命を変えるべく、ゼクスはカロンを正しく育てようと決意する。無能と蔑まれる無属性魔法の適性持ちだったゼクスは、カロンを守るために前世の知識で新術式を次々と開発!常識破りの力を手に入れ、カロンにも正しい魔法の使い方を指導する。さらにカロンを狙う王宮のスパイを看破したり、カロンに愛情を注いで闇堕ちを防いだり、不安要素を払拭していき―!「お兄さまのお役に立てたのなら本望です!」「やばい。オレの妹、めちゃくちゃ可愛い」良い子に育つ妹を今日も兄は溺愛する!世界最強の兄が最カワ妹の破滅回避に挑むハートフル・ファンタジー、開幕!