Orihime always has been the bigger NTR bait than Hinata since the Fullbringer arc. That arc lasted what, two weeks in-universe? Orihime got "cut" by Tsukishima and his Book of the End in second day or so of that arc. And then she spent two weeks under his total control, by the end she was even protecting Tsukishima from Ichigo.

This was such a perfect setup for NTR. Tsukishima could have changed her memories to make Orihime believe she agreed to date him in exchange for the Fullbringers help in recovering Ichigo power. And then he would just keep pushing the envelope, constantly getting Orihime to do more and more lewd stuff, and all the while she would hide it from Ichigo because Tsukishima said "Ichigo has enough trouble already, let's not ruin his only chance to recover his power by revealing our relationship".

Orihime would reluctantly service Tsukishima at first, since she would feel something is wrong, but with Tsukishima helping her "create" new memories by pounding her pussy into a sloppy mess, her reluctance would eventually give way to enjoyment and lust.

The ending would be different, instead of stealing Ichigo powers, the Fullbringers just leave, because Tsukishima convinced everyone that Orihime is the real prize because her of her healing powers. But the truth is that Tsukishima just wants to keep having baby-making sex with Orihime.