Until the siren pulled Katsuki as hard as he could without hurting him into his chest, holding him close and stroking his blonde locks as he sang him into sleep
R: "H-HEY!! COME BACK HERE!!"
Ren's lower lip quivered. He then bit it as he looked at the Siren leave, he looked down at the water, slowly backing up onto shore. He was too afraid to go any farther. Denki on the other hand couldn't just see his best friend get taken by a siren. He went deeper into the water, chasing after the siren. GO DENKI GO-
D: "DAMMIT!! UGHH-"
He sighed, as he swam back to shore, giving up..he felt..horrible..I mean, he just witnessed his friend leaving..just because he didn't save him on time..Ren was waiting on shore for Denki, when he saw that he didn't have Katsuki..he was heartbroken. He didn't have a crush on Katsuki or anything like that-but he cared about him.
D: "I-I tried-I couldn't catch up with that stupid Siren-"
"....I-It's fine."
You know it's not "fine" Ren.