Chtholly Nota Seniorious

A leprechaun. She has the appearance of a Markless.

Was the oldest fairy, and also the wielder of the strongest sword of the Regal Braves, Seniorious.

As extensive use of venom, her hair started changing to a red color and she experienced slow memory loss.

She is deceased in battle. For those wanting to pick up the Light Novels, it is Volume 3, Chapter 4 Part 5.

Seeing Ithea's history it can be inferred that leprechauns loop-reincarnate which means what happened to Ithea/Aiseia could also happen to Chtholly/Kutori.

The scene in Episode 12 of the anime is a flashback of Chtholly/Kutori's birth, not a reincarnation.