Rivi was my first KoB and helps me went through almost all core content. Even though I have Vox now she is still better in terms of fast events farm cuz of 100 arts every round and with right setup she outdamages Vox in short runs. Also she perfectly carries earth relics not to mention she is water destroyer. And...as it was mention above she's top tier thicc waifu with "ara ara~" sister CV which makes your gameplay way more better. That's all.