For visibility, a note has been added in the Main Menu indicating the Early Access version.
https://store.steampowered.com/app/1841150/Hitori_Kakurenbo_Online/
Early Access note in the Main Menu
Source: Steam Community (opens in a new tab)
Build and release context
Recorded Steam release date:
Within one calendar day of this post (UTC). The listed date does not establish an exact launch time.