Am I the only one who thinks dude has been forced by pretty much every single narrative point possible into the Amano route?
I get it, she's cute, gorgeous and her personality isn't bad, but in regards of the MC, he wasn't just being passive here. He was legit not interested in Amano as a romantic partner. She was nothing more than his boisterous childhood friend. The kind of childhood friend that never wins in romcoms.
Maybe the reasons because there are so many NTR doujins is that put it simply, they don't look good together. Her feelings have sure blossomed, but his? Besides normal teenage lust, and the over-protectiveness of an almost family member there was nothing to tell MC loved her until the cliched "aw, she's going to get taken away from you."