Short answer
Yes. Aniimo is listed as free to play on Steam and official launch materials. There is no base purchase required to add the game from its official storefront.
What “free to play” confirms
The label confirms the entry price, not the absence of a store. Launch reporting identifies paid cosmetics and bundles. Availability, contents and regional pricing should be checked in the live client or official storefront rather than copied into a permanent guide.
A separate monetization question
Whether Aniimo uses character gacha is a narrower question than whether it is free. Pawprint’s executive producer said obtaining Aniimo would not use gacha, while the live game still includes paid items. See the monetization page for the source boundaries.