Hi there! We're currently fixing this, sorry for the trouble you both had! Our testing hadn't shown this issue so we didn't expect people to have trouble with it. We should have another version up in a couple of days!
In the meanwhile, just in case it helps, drinking the rainbow liquid item and having Sai in your party gives you 3 total HP rather than the initial 1 HP.
(But make sure you are playing with version 1.0.1 or above)