#first person protagonist calls when they get reception is arven

[applesjuice]

What was the worst memory Akari remembered ?

It's less one memory so much as recalling how they treated others before getting sent back in time. They have vague recollections of treating the other students of BB Academy terribly in order to get stronger and are under the impression they were a terrible person. They actually don't remember the Terapagos blast (but Carmine and the protagonist sure do).

So Akari rationalizes all the crazy stuff in Hisui as them deserving it. They've kind of trauma bonded with everyone there because it's like "Akari go do x dangerous thing" and they do it and then are praised for succeeding, even though they had lava flung at them or were attacked by giant feral monsters. It's messy af and more than just one particular memory that is a bad time, so much as an accumulation of tiny instances they've recalled shaping their perception on who they are any why all this is now happening. Pretty much a child trying to rationalize bad and scary things happening while putting on a brave face.