how to get all the servants in “just kill me3”

[ikisugita]

play store link:https://play.google.com/store/apps/details?id=com.fundoshiparade.bokukoro3jp&hl=en

version:18.4

I could not find any flags for possession of servants, although I could manipulate currency, items, and the level of servants.
There are characters in this game that are only released from limited time summonses.
Perhaps there is a way to make that limited time summon always appear.

please help @NoFear

-Translated by DeepL