Well, shit happened...
here are some theories/speculations i currently have with how the Suo-arc is going;
1. One of my theory on Suo's sudden disappearance is that he was originally planted in Bofurin as a spy, but he later grew attached to them, in which the side/agency/family (presumably a mafia/yakuza of some kind) he was working for/with noticed his strange behavior.
And so they had to call him back, but most of the members didn't fully trusted him, so he had to prove them. Also also he was worried they'd investigate his relations with his friends.
And maybe that's why he had to confront Nirei, since he was also like his student, he would know all his weak points, ending the fight quickly, making it clear to whatever faction doubted his loyalty and bcs i do think that he was being watched by, so his action of fighting ultimately won over their trust, that he is still more than capable of taking down any enemies they'd have facing in the future.
2. So, during the fight, when coming to middle-end chapter, Suo was initially thought that he (Nirei) wouldn't preservere as much as he did. Which he was proven gravely wrong, Nirei was able to land an actual hit against Suo, he was very surprised and somewhat proud of him, but unfortunately since he was being watched (as previously stated), he couldn't say/praise him anything for it.
How am i so sure about this specific theory?
3. In the final-esque panel of the chapter, we get a glimpse of the barely conscious Nirei propped up against the wall, and for a second, it seemed that Suo was wanting to take off his coat to cover Nirei. But of course he remembered that he was being tailed/watched on, and instead prompted for a subtler approach; Placing a piece of leaf on his head.
Now, you might be wondering what could have that ever mean? Well, after skimming a few text on symbolisms. Apparently placing a sprout, or in this case a leaf on someone's head symbolizes personal growth, an where did this cultural symbolism originated from? China.
I rest my case.
P.S: if any of my theory have or been stated in some other past blog/articles before, i swear i didn't know them before posting this :(