It's about time I make this.
Joining the ranks of CALY.SIS and Jackal Kitsunami, I-D is gonna be a music persona, handed off to our favourite eldritch horror Sebastian The Shapeshifter. The Theta-Delta fits mostly because:
A) The original context is that the name was based on INFINITUM, a Sonic Fanfic based on a Wolf MC who struggles with his identity and past life
and B) Sebastian isn't just a shapeshifter, he's a whole mattershifter. He can change shape, size, anything, no matter what the assumed limitations. Hell, his normal form certainly isn't his true form.