To be pedantic, yeah technically what happened isn't NTR (Netorare). Netorare is when someone's lover got stolen. For NTR to happen, someone have to be the heroine's lover and her brother isn't her lover. So far she's shown to be single, so whether she's been ganged or not, NTR can't happen because she's single.@BuyVelomobiles
Something really nice is going on the authors twitter. It seems like after "someone" made people get their attention about what really happen offscreen he finally started to speak about it. You should take your time and check it out yourself, perhaps if you also really angry about it leave some meaningful comments (not like me lol) but here is what he said:
"I learned that if you can't understand Japanese, it becomes difficult to understand." (Probably to me where I said to another user with showing pictures what really happend offscreen."
"From people in other countries that have been illegally uploaded, We continue to be attacked... I'm basically ignoring it, but The destructive power was so great that I lost my nerve, I wanted to share... If you don't know that Egaki is such a shitty positive person that he'll die, I deleted it thinking that it would just be an exposure."
"To gal sister of pixiv, I am being harassed by adding NTR tags without permission, but I took a screenshot of it, People are going wild and saying things like, `This is proof that this work is NTR!'' and
`This is also the case with Fanbox and illegally uploaded works! This author is incompetent! He's brain dead!'' and it's very troubling. Strictly speaking, it's not NTR. Egaki, who loves NTR, says this."
"I carefully explained the intentions of the project to the DM attacker. It seems like the translation function isn't working well, so I can't understand... I was in trouble, so I'll ignore you. already. It doesn't get across. I've given up. Sorry. foreign people."
"Something that was deleted due to violation of Fanbo's rules was uploaded illegally, The URL and image have been spread and it's out of control. I can't stop sweating" -> lol
"I asked him to give me a new title, but since the title has the potential to be an erotic manga, I decided to use it as is. I wanted to share it."
"From people in other countries that have been illegally uploaded, We continue to be attacked... I'm basically ignoring it, but The destructive power was so great that I lost my nerve, I wanted to share... If you don't know that Egaki is such a shitty positive person that he'll die, I deleted it thinking that it would just be an exposure. sorry"
Edit: Basically this fucker says its not tEcHnIcAlLy NTR lol.
This's the point author was trying to talk. And she's actually right on this point for defending her work as not NTR.