Okay,
1) ingest what's essentially the used condom containing a part of Zero's being.
2) get hard.
3) bone her.
Seems simple enough once you get past the first part
He just need to have that fetish of eating his own cum out of condom in the femdom/SM/whatever relationship where either girl would force him, or he himself would? Hard to say, cause its so not my fetish I often switch off/close anime/manga/porn if I stumble upon such "depravity" - so I don't learn the whole plot and thus have no clue what type of relationship has that in it
Also I kinda started reading this in like chapter 45? After some manga recap video I wasn't that much interested in. Frankly I have little to no clue WTF is happening beyond people dying and reviwing and changing worlds, there being a lot of sex and some dude who seems to want to kill nearly everyone to get his own waifu back or something where he would even "endless eight" style rape-torture people. In all honesty if this was DMCA style purged, I would probably forget it even existed in less than a month.