I really don’t get the NTR label being thrown around here. It’s a fucking dildo. It’s more or less there to help Mako get a better understanding of her own body, as well as her approach to sex with Shinichi. It’s very likely that the end of this arc will be of Shinichi and Mako having sex, but they’ll actually both cum together. Ya know, like in hentai.
Honestly, this is something I’ve never fucking seen in manga and I’m glad the series seems to found a way to remain interesting. I thought there might’ve been nowhere the series can go after the sex barrier.