Come on Myth mongoloids!
>Myth Shocked to Learn JP Holos Dropped Senpai/Kouhai
https://www.youtube.com/watch?v=haP20sHlBf8

One of the biggest "tropes" in JP medium is when people separated by hierarchy grow intimate enough to DROP the formalities and address themselves as "chan".
For instance, here is when AZKi was FINALLY given herself permission to call Sora "Sora-chan"
>The moment Azki started calling Sora as Sora-chan
https://www.youtube.com/watch?v=uEeXFhw2TyY

Myth are around for long enough to understand that, for the girls they're close enough they should have dropped the "senpai" a thousand years ago!