 If you liked
Mahouka Koukou no Rettousei
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 ...then you might like
Kasou Ryouiki no Elysion
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The mc in both are both overpowered and have been involved in traumatic stuff however both are inept to a degree while both mc's have a little sister that loves them and are considered geniuses in their school and in both cases the siblings just got reunited again after a forced separation. In Elysion's case unlike mahouka however the incest bond between the siblings is quite close to real. (Actually I don't know in mahouka since I haven't caught up but judging by the pics it hasn't happened).