dunno man, i have a younger sister too. but never cross my mind to take this path since i felt nothing 🙄 and yes, i adore her and im a doting brother too. also overprotective one 😒😏
this manga is very nice for change of pace, sometimes i got bored from easy peasy isekai or reincarnated life, the journey of lame/regular/lucky af person to the harem life, over underestimated person become the strongest of all ┐(´д`)┌