Since Gal knows Hisui and Akiha, thiiiis could definitely go somewhere! I know Abyss canon as well, so similar situation buddies unite.

Kohaku attempting to find peace with herself in canon resulted twice in suicide (recovering after her second attempt with convenient amnesia) and one single, good end, so I'm hoping the power of friendship~~ (or at least help with her damaged psyche) will do a thing or two for her revenge complex here.