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Select a chuuba.
She becomes real and starts living with you.
But she will appear as her avatar self, not as roommate.
For example: if you choose Gura, you'll get tiny shark girl, if you choose Ina, you'll get tentacled priestess, if Sana - a fucking goddess of space who may accidentally destroy our planet.
They will behave according to their lore as well, and its often not like the girl behind them during streams.
Remember: in reality they may look not as cute as their simplified anime appearance.