>>32504372Pekora and Koyori were mostly on the same team for most of S2, and they joined up with Suisei's team for the last battle.
Pekora wanted the final to be them against the world, and gave her a note explaining that she would betray them soon, but Koyori's inventory was full so she couldn't get it and read it in time, so Pekora had to take back the note and go solo when the time came.
Koyo was confused and tried to walk into her base to join her but just got shot dead multiple times since Peko was on "kill on sight" mode. She reluctantly ended up joining the raid against Peko with the rest of the Holos.
After the end of the season she found the note and realized what happened, and it was an anime level dramatic irony moment, so a lot of fanarts started pouring in of that entire arc.
There's a reddit post that had exact timestamps.
I don't think any translated EN clips covered this yet, but Mechanico probably will.
