Hi you can find it in Lower Peridot ward after the city renovation (beat Ciel)
This is the information on all current Pokemon,
https://www.rebornevo.com/forum/index.php?/topic/42836-void-kissed-pokemon-location-guide/
it has time of day found by city
LMAO just realized that it said evolve, if you look at the Solosis guild you will be shown where the key is in the current episode