The ML, and some others, have a disease in which they lack empathy/feelings for other people. The MC enters different worlds with the ML, as a sort of healing process; so the ML can start to feel again.

In the final extra you'll see how much the systems love him. There's multiple systems, with a new one supposedly being assigned in each new world.

**The MC dies at the end of every arc, some deaths/aftermath chapters are better than others.**

First arc: Prince (MC) & Shadow Guard (And then Emperor)

This was an ok arc, wasn't the best one in my opinion. The ending was expected but it was also the only arc to lack an aftermath chapter, maybe the author was warming up?

Second arc: Teacher (MC) /"Adopted" Student (And then overbearing CEO)

I liked the MC's death the most in this arc, I had tears in my eyes, but I'm a sucker for this stuff. The ML keeps the MC locked up near the end, which also indirectly causes his death, something he never forgave himself for.

Third arc: Futuristic/Interstellar Arc: Death Row Convict (MC) /Planet ML (Spiritual representation of a planet)

The best part about this arc is the ML trying his best to act like a white lotus. He read it in a novel he found on the planet, presumably from another death row convict. He's not the best actor, however. (The MC knows he's acting too, as he gets to see the plot overview.) The death is a bit lackluster... probably because it would be hard to come up with a realistic reason for him to die.

Fourth arc: Swindler (MC) /Feng Shui/Spiritualist Master (This arc is very similar to the author's other novel, My Five Elements Lack You. It was ok, but probably would've been better if I hadn't already read that one. I believe this short arc was further expanded into a new story?) Not going to talk about this one much as to avoid spoilers for that novel.

Fifth arc: Little Stalker (MC) /Doctor (And alien) This was probably my favorite arc, as the ML seemed to be the most interesting in this one. It's also the arc in which the MC seems to completely bend. His death in this one can also be quite sad, but the site I'm currently reading this from (with mtl) seemingly cuts the chapter off at the end. I'm not sure if that was the author's intent, or a problem with the site, but it caused the arc to fall short a little.

Sixth arc: Scammer/OldHuman (MC) /Higher Ranking NewHuman (Not sure if they actually belong to a high ranking family as we aren't given specific information, but that seems to be the implication.) This arc was quite long and a bit boring overall in my opinion. It just wasn't that interesting setting wise, but that's subjective.

Last arc: Spiritual Radish* (MC) / Immortal (*He might not be a radish, but that's what the mtl translated it as.) In this arc the MC and ML switch roles, as the ML wants to prove to the MC that he wasn't just using him to heal his disease. Just an ok arc overall, nothing special; and a boring death.

a person who doesn't/cant feel or show emotion

ML is MC's first love but he found out that his (MC's) first love that was describe as a cute girl with pigtails/ponytail is actually a boy and has bigger... //cough, this might not be so much spoiler since it was found out after the first world

There's a clear reason why MC needs to do these tasks, ML is actually part of a very very small percentile of humans where they can't feel feelings, they usually live up to 30 and dies because of lack of emotional attachment to continue living. MC (and other co-workers like MC) are the 'medicine' for people like ML. It was also explained why there are failed missions or low evaluated missions AMD why MC has high evaluation every after missions he finish

especially finally ML learns his lesson that forcing someone is bad, I was glad he felt the pain of his consequences