I appreciate that this is one of those rare futa doujins where the plot isn't basically "Holy fuck, dicks are AMAZING!" But on the other hand the presence of the dick is a bit baffling as there's no real reason for Rin to have one in the first place. You could do the exact same scene without it, and nobody would realize. So...really, why bother?
Why does futa get scrutinized so heavily compared to other kinks, geez. You barely ever see comments like this on basically any other tag, yet every futa doujin I click on will have at least a couple of people asking why it wasn't just 'regular yuri' or whatever.
It might be a bit shocking to people on here, but there are authors who like to draw futa - some prefer to draw it over vanilla yuri or het, some just like to draw it alongside their other works. So they do. it's literally that simple. They liked the idea of a futa story with Maki and Rin (not a yuri one or a genderbent one or anything like that) so they drew it.
And people saying "hurr the author only picked rin cuz she looks like a guy!" are really reaching hard for something to criticize. Not only has Bocha drawn vanilla MakiRin before (so it's obvious they're just a fan of the pairing in general), but there's plenty of futa Love Live doujins about basically every girl and pairing, yet as soon as it's the tomboy it's suddenly a grave sin? (lol who am I kidding, futa itself is a grave sin to a lot of the more fanatical yuri fans anyway)
Like, just stop. It's a kink. It's a pretty damn popular kink in ero doujins. There's likely no deeper meaning to any of this besides the author finding a futa ver. of this particular pairing hot.
Also sorry if this got a bit heated, it's just been bubbling up for a while since it seems there's the same damn comments and criticisms (or outright bashing) on every futa piece -_-
I wouldn't go so far as to say the author is getting hate for this. Rather its just a lazy, uninspired choice to slap a dick onto a character that is the least fem of the LL girls. It doesn't fit any kind of narrative, and certainly not a transgender one, reiterating that the author has no such intent and it is - as you say - just a fetish. However, unlike a decent amount of other fetishes, futanari can easily come across as harmful to the trans community. Futanari fetishizes, and at the same time, erases transgender people from representation in media. It turns the transwoman's body into a deviant desire, and acts to dehumanize real transgender people in the eyes of the media consumer.
So yes, when there are the number of trans people that use these forums, there is bound to be active discussion in these threads. To many trans people futanari is not just a harmless fetish to be hand waved and forgotten about as it can have a social effect on how people view them. That said, many of us are old and tired and accept that there is just not much media with transgender characters, so while futa isnt ideal, it can act as a makeshift outlet sometimes. So instead of being angry, I would just rather discuss/critique etc. Its more fun that way. And less exhausting.