Hmm...
1- The mountain spirit theory, which seems to be very close to canon and I hv shared as much as I could on it in other others from 2-3 days back. Also I learned abt it from a kr fan who deactivated.
2- Related to Taeuk coming back to the story. Since he has been confirmed to be coming back, maybe my theory will? Or not. But here goes nothing-
I believe that mole guy (Shim Changhyeon) trying to get closer to Cheol is sus. He even said smth that sounded weird and sus in ep 74, when Cheol was busy ensuring that Miae didn't run into them. He was very concerned abt whether he'll be able to get closer to Cheol coz Miae could ruin his chances for that if they hv a special relationship. We saw him later threaten Miae using Cheol to not interfere with Songi either, and we can see that mole guy copied Jinseop's style. It could be that aside from wanting to date Songi (on the last day b4 summer break he even said that he'll make sure he has a gf when they return to school so I hope she's alright), he also wants to ensure that he's on top of the social ladder in school, and usually charas like him do that by joining bullies. Since we hv seen him bully Miae every chance he gets, he surely does that, and one bully group that we prominently see is the one Seop hung out w, which also included Goguryeo kids (we can see it in seopmae downtown date eps). And Seop was the one who tried introducing mole guy in ep 71 to Cheol as well, so it's likely he's already part of the gang. Here's what I think - mole guy is actually kahoots w Taeuk's ppl, prolly smth like a spy too. So Taeuk must hv already known abt Miae. Then that moment in the school trip when he threatened her also isolated her from Cheol, so it's likely that Miae will be targeted more until they finally target her separately when she's w/o Cheol. Maybe the cliffhanger from 159 is a confirmation for that, that they hv been trying to separate them to target Cheol, coz Taeuk had promised that he'll get back on Cheol by targeting everyone he holds precious. And I dont think Taeuk's moving alone, coz even if that bully Inuk said that no one's in contact Taeuk anymore, it's likely that the group has become smaller instead. Also the one who stepped on Cheol's bag during the school trip might be one of them coz the flashback of Taeuk's group bullying Honggyu showed a bully hving similar shoes (and mole guy is too cowardly and doesn't hv that kind of malice to do that to Cheol).
Another part of this is more like a wish, but I hope to see Jang Seonyeong back in all this, as an ally to Miae and Cheol (w a face). This is because during cheolmae forced separation arc, mole guy and more ppl seemed to approaching Cheol alongside Seonyeong, and the girls she hangs out with also seem suspicious, esp since Seonyeong revealed the name of the headband girl (Eunmi). It feels pointless to reveal a chara's name to not hv her appear again after that.
And another part of this theory is that this whole plot will help resolve Cheol and Honggyu's trauma, with these bullies finally getting justice and Cheol not being afraid anymore. That he'll ask for help from the adults or receive their support this time, to make sure he isnt alone. And Miae will also show a lot of development by the time this plot gets resolved, which I think will be along the lines of her trauma from her unpleasant past that was revealed in 148.