The Art Dump

The cat disciple (unnamed for now, and maybe even in the au for a long time) was born in the cult only one generation after the Lamb accidentally killed Narinder and, seeing potential, the Lamb took them in and raised them themself. The black cat follower always knew what their intended fate was, even if the Lamb couldn't explain it (the vow of silence had been done long before the cat follower was born), and was happy to work hard to be the perfect sacrifice and future host

Unfortunately, the Lamb's attempt to offer Narinder's soul a host failed, and the cat follower returned from the afterlife still with their own soul, along with an extra tail granting them immortality (not that anyone knew this at the time). The Lamb was devastated, and in a fit of renewed grief killed the follower before running away from the cult as a whole. The cat revived on their own, and was themself devastated that nothing had gone according to plan. It took ten years for the cat follower to find the Lamb again, and another five for them to convince the Lamb to return to the cult the cat had just barely managed to keep together in the meantime

By the time the Lamb had returned, they'd found the last fragment of Narinder's soul, and had shattered their own to make an unbreakable lantern to contain it. The crown was also by now permanently stuck in it's sin form, and only able to turn into a pair of dual sickles.

The cat dedicates themself to helping the Lamb find a way to revive Narinder, and even after the failed attempt at being made a host they'd still happily sacrifice themself again to achieve the Lamb's goal. They're unfazed by the concept of their death, they die many times in many ways over the next few hundred years, and the idea of permanently dying (or being forced out of their body as the case may or may not be) isn't any different. Living hundreds of years past your planned death by sacrifice and first death by murder does that to you

Due to their status as a nekomata, the cat is one of the only beings capable of connecting with the Lamb's fractured mind and hearing their thoughts without going insane themselves (though it can cause quite a bit of pain, even when the Lamb actively welcomes the intrusion or initiates the connection themselves). This makes the cat the only one to have heard the Lamb speak in any sense since Narinder's death, and they are the only one the Lamb would trust to hear them, insanity inducing mind aside