At first glance of the first chapter, this manga easily could have went the typical two/three chapter route about an incestuous unrequited love that would lead to some small misunderstanding (rape possibly included), followed by a rushed and unconvincingly conclusion that the feelings are mutual, and the older brother's woman phobia would be completely glossed over. However, as it progresses, this story surprisingly gets pretty dark, sad, and complicated with a lot of character development. Their feelings seem geninuely real and all you want is for them (particularly the older brother) to be happy.
On a side note the older brother is so fragile and damaged and adorable how the fuck could you not instantly fall for him and want to protect him from literally everything???
3-pun Instant no Chinmoku