@Tcof
NTR is the act of a significant other being taken away (willingly or unwillingly) or having sexual relations with another person (willingly or unwillingly), usually behind their other SO's back or even in front of them in some circumstances. In this circumstance, it is not NTR, simply because there is not a lover relationship between any of them really(yet), so there is no one to be taken or to be cheated on. Senjo can go with any of them, and the others won't have anything to cry about because she isn't theirs. Until either Takamura or Hoshi confess and Henjo accepts, her going with another person wouldn't be NTR.