LN reader here, what can I say is... this is so different from the LN, I don't know about the WN but, why the manga artist make the characters so pitiful? even giving the mc and imouto unnecessarily struggle, especially adding those cringy lines.
c'mon imouto where is your prized weapon Lightning and Fire Dual Hammer?
how it look like to me. is they try to push the childhood friend to be more likable.
also imouto literally hates her. the childhood friend is actually pretty manipulative. mc fails to see that.
a theory i have is that the original premise between them is actually wrong. sinds you only hear it from her side.
who knows maybe he was a super secret character only recruitable if you do some abstract route. like not recruiting the first recruitable character/the childhood friend or associating with her. and seduce souta. like making him give up on her. getting him to lose weight by lvling and turn handsome. is a pretty good secret character for a game.
but because no one likes him, no one(but maybe 1) tries. cause of the premise the childhood friend told the player and everyone else.