i have a feeling that you don't really read it...from chapter one clearly show that SHE IS her blood sister...not adopted sister...
and we don't know yet about her sister as his harem meber...there is no clear action that he saw her in romantic way...he saw her in adoration way...and for your information, adoration different with love...
have you been paying attention to the trend?
were no longer in the era of miyazaki where there any relationship a boy and girl don't always have to be romantic.
unfortunately no my friend...
we are at the era where any hint of attraction is equal to romance, blood relation/age/logic be damned.
It is the era of merchandising, limited edition figurines and ....fk toys....
the decency of story telling has now ended, you can't sell anymore without those.
nope, i don't think so...all author has his own style...and all i know that harem is trend(at the time this manga released)...its true some with blood related end up as harem member but i find a lot of other overprotective and pamper his sister MC but when his sister confess, he turn it down...for example mushoku tensei, MC really adore and overprotective with his sister...but did she become his harem member? no!...true that harem is trend, but not about blood related...and its japan manga you know, in japan brother-sister blood relation is frowned by majority people...so, only an author that can handle the pressure can make that story (love with sister-brother blood related)...
in his harem party lol
no blood relations equals no hesitation for a fk.
Dropped to the bottom of the ocean where (╯°Д °)╯╧╧