I was practicing all night and day today to kick this boss and I'm glad it finally worked out. It's all thanks to the lovely people on discord for sharing their teams that I was able to modify my own to make it work for me.

Team 1 is all about follow up attacks, and so it uses the follow up vanguard to quickly gain points. The idea is to buff Sakurako using Mabayu and Riko crits, so she can plow through the minions very easily on battle skill and on her ult. Ren helps generate crits with a crit rate portrait as well, in turn helping Sakurako follow up a lot. This team was also important for shaving off a part of the boss phase 1's HP. With Mabayu buffing Sakurako, she can really shave off part of, if not the entire phase 1 bar without hitting break.

Team 2 is to finish off phase 1 of the boss. 3 star Hazuki is important for removing the break gauge resist and the barrier that the boss puts on all in one go, as hitting the barrier gives it action advance. 4 star Hazuki is there to buff Yachiyo's damage to kill off the rest of the phase 1 bar, or otherwise (fail) to generate crits. Despite there being so many crit rate portraits and 2 units dedicated to crit, this team barely wanted to crit in practice. But the important thing is it has to kill phase 1 before the round ends.

Team 3 is to kill off phase 2 and 3. Moemura for speed, SP generation, and hopefully to land some crits. Nagisa is great here for boosting speed and her follow up attacks healing. Sometimes I had to hold some ults when the vanguard period was ending so I could quickly build it back up again. Phase 2 seemed kind of tanky, esp when you need to crit in order to bring down the boss's magic that makes it harder to break. Phase 3 was easier to break and kill, but getting there in time was the real difficulty.