The setting takes place in an alternate timeline one year after the disappearance of Quiet Zero. Mainly, Suletta's health gets better much more quickly than in the original story. This is aimed at those who can withstand vague settings... If you are fine with that, I hope you enjoy it.

Vague chronology

Quiet Zero's disappearance

Here

About a year

Summer vacation

This is in reference to a school from an English-speaking country, not a Japanese one.