ヤンデレ化を回避したはずの天使な義弟は期待を裏切らない

Duke's daughter Adele remembered—this is the world of a novel, and she is the tyrannical villainess who caused her stepbrother Nikolaus to fall into darkness. However, by staying by his side, pouring love into him, and protecting him, fate changed. Nikolaus grew up to be a completely gentle and calm gentleman, and he should have avoided falling into darkness... but why is he trying to keep me from leaving, instead of the heroine――!?