Here's the trick, anon. Never prefarm for any character. Don't farm their echoes, their asc mats, their upgrade mats, everything.
If you do, you're obviously letting Kuro know you're planning to pull for that character, and they will slide your UID into the LIONED list. If you don't prefarm anything, Kuro won't be able to tell which character you want, and you will easily beat the 50/50 system. You can thank me later.