The game is paid, but testers don't have to pay.
To join the official google play closed test, please join this group and follow the instruction:
https://groups.google.com/a/slayers.zip/g/stg/c/cB5R46JWeC8
It's just a couple of clicks and you can have a lot of fun.
Yup, very uncommon nowadays, a game made with intention to bring joy.
In other news, it seems nobody knows how to make a paid google play application available for closed testers without a payment other than running a sale, but you can't do it permanently.
Well, I've figured out a better way.
And I will gladly share it if/when I pass that testing requirement.
PS: most frequent question I get is what do items do.
While figuring that out while reading jokes is part of fun, I've written this article for those who can't have fun without spoiling the discovery.