Judging by some of your other posts, I think you're pretty safe if you're looking for a manga without romance. Even in ONE's other super popular series (Mob Psycho 100) where the main character had a crush on a girl, it's not reciprocated and it's used as a tool to delve deeper into the inner workings of all of the characters themselves. Deep, realistic, upfront, and ruthless dissection seems to be ONE's bread and butter when it comes to storytelling. I think if he was going to write something where romance was critical to the plot, it would be telegraphed extremely early on so that he didn't have to waste time building up to it.

There's definitely bits for people to pick at if they have a ship they like, but it isn't necessary that you read anything that's happened as strictly romantic and it still keeps its meaning if you see all of the relationships as platonic. Given everything else he's made I don't think it's terribly likely that's going to change. (And at least with the direction the webcomic is going, it really doesn't seem like there's even going to be time for anything like that to happen.)