Brother, Who Am I?

System, Adoring His Little Sister, Urban Fantasy, Plot-Driven, All-Rounder Protagonist

I'd like to read something like "Soul Transmigration and a Dot-Cing System: Unlimited Spoiling". You transmigrate into someone else's body with a System, dote on your younger sister like there's no tomorrow, and get sweetness, comedy, and investigations, plus... you'll have to read it yourselves.