Sakuramoria

Does this cost gold or is it just a mandatory event?

It is taken into account when calculating the quarterly rank.

Do I choose the gift myself?

No.

Is this for mages or for everyone?

For mages.

Added 6 minutes later

While searching for more books with more tips on leveling up, Varya enters the "Exchange Point" in the first week of September.

At the exchange point, Varya discovers (who would have thought) Oleg talking to an employee.

— So, no one bought it, huh? Well...
— What did you expect? 10,000 reagents is not pocket change, and there don't seem to be that many patriots in this academy, heh.