I mean i guess in story sense, you'd call it netorare, and in player sense, you'd call it netorase if you knew it had it in it.
And that's only if you don't know what truly makes something netorare/rase. The entire story so far she's been reserved and pushing you away. You insist do she just goes with whatever you and your sister wanna do with her. Which isn't anything sexual, literally just hanging out. When your character first meets her, he finds out that she saved your sister, Yuka, and your sister recounts everything that happened verbatim. Which includes Chika mentioning she's a prostitute. Apparently everyone treated that as simply a rumor, later on she pretty much has a drunken breakdown, offers you sex which you can refuse, and after that you see her leaving a hotel with a guy. It's not based on your actions and even by the hater logic, it would only be seen as ntr if the hotel scene is only triggered if you have sex with her. It's not. And even then, by the definition of ntr, still not ntr.
There is no exclusivity claimed here. She says she's a prostitute, she makes it clear she'll stay a prostitute. People calling that being cucked need to go and actually meet someone for once.