Anima

When it appears

Once you've completed The Extinction Project, found the four CHAOS discs (Fulmina Disc, Gurgita Disc, Anima Disc and Agita Disc) and taken them back to Laboratory of Diseases, it can turn up anywhere in the wild in Precursor Valley, the Abyssal realm (maps 477 to 529). It stops turning up once you own an Anima, unless you've completed the main quest Destroy Vados and taken Eliza up on her offer in Hilda's Room.

Capturing

It has no favourite foods, so each food adds 1 to your capture chance, and Perfect Berry 10. As a Legendary Nexomon, it's harder to capture: food counts for less, Nexotraps count for half, and wearing it down adds at most 10 instead of 20. A Golden Nexotrap still adds the full 100. Catching a Nexomon explains how the whole chance adds up.