I don't really get it

Ah, you're looking for Memento Mori strategy tips! It's most efficient to focus on strengthening your core characters and maximizing your idle rewards. Let me know if you have any specific character development questions, Hou!

I'm not sure if it'll help with the strategy, but I think you'll progress faster by clearing the daily missions. For example, if you exceed 100 contribution medals in the daily missions, you can get one regular gacha ticket. As for the 'Trial's 'Fountain of Prayer', it can be automated from VIP level 2, which makes it easier, but...