Y'know, I wanted to like this thing. Based on the description, it looked like it'd be a Netorase VN with the guy being the one being shared, rather than the usual... and it IS that to extent... except it doesn't play the theme very much. It's like the writer didn't want to properly commit to the theme somehow, and ended up wanting to transition into a fairly generic harem thing partway through... but they don't quite commit to THAT either, leaving it somewhat unsatisfying for someone like me.
To an extent, for me, I suppose part of the problem are the characters. The MC and the GF are supposed to have been in a relationship for 3 years at the start of the story... but they don't ACT like it. They behave more like a couple that just had sex 2 days ago rather than a pair that have supposedly known each other for a long time and been sexually active for an extended period of time. It's not just in how they act with each other during sex... bland sex-lives for an extended period of time are not an impossibility or even uncommon, but rather in how ridiculously shy they are around each other, and around the fact that even perfectly mundane things don't seem to have happened naturally, like the fact that the MC apparently didn't experience much of Shiori's cooking or had her cook for him often.
There's a bit in the Misa route where they cook together and he's all surprised about how well she peels vegetables... and it just seemed so weird. Are you seriously expecting me to believe that this was the first time this could have happened when they've been together for 3 years, and at least one of those while they're college and living in their own apartments? Really?
Basically, the two SAY they're a couple and the MC keeps spouting off he loves her and yada yada, but the VN thoroughly fails at showing us that they're a couple if favor of showing how much of a moeblob the Shiori is.
In any case, I was only able to read Misa's route to the end... as much as you can call it a "route"... it doesn't even have a real ending tbh and it chickens out at really showing her feelings and motivations in the whole arrangement. It has some moments near the end where it looks like Misa might be trying to either steal MC from Shiori or try to establish herself as a more permanent part of the relationship with the both of them together, but the story again doesn't commit to anything and leaves things ambiguous in terms of how things might develop aside from her mentioning that she's starting to get addicted to sex with the MC, or perhaps the situation with the two of them in general... again, ambiguous. Super annoying...
After that, I kind of got bored and just used the good ol' CTRL key to unlock everything else.
At the end of the day, this story feels more like it was designed to be an easy excuse for a guy to self insert in a situation where he can have sex with a bunch of girls, rather than actually focusing on the netorase or cuckolding aspect or whatever. It doesn't really differ much from a more typical harem game aside from the fact that the main push for the harem comes from the GF rather than the MC.