Not sure on the exact requirements, but I think you do need everything gameplay-related unlocked: all arcana cards (with max grasp), weapons, keepsakes, companions, and max vow of rivals. It might also be related to completing some number of chaos trials.

Edit: apparently you also need 10 underworld and 10 surface clears, and unlocking max Vow of Rivals is only required for Great Chaos trials and not the 0 fear ones.

Thankyou for the comment. i do think i have 10+ clears on the underworld and surface (i've clear them hundreds of times in total), max vow of rivals both on the underworld and surface is done aswell, arcana cards are maxed out, unlocked all weapons, and companions. altho my concave stone isn't there yet (i can't give echo gift since the start of playing hades 2), all chaos trials also has been completed

i just got concave stone (i legitimately thought it was bugged on my end because i can never give nectar to echo) i asked in another discussion, turns out it was just me being stupid leaving after getting echo's blessing EVERY SINGLE TIME i encounter her (can only give her nectar after accepting her reward)

now i got the randomizer. thankyouu