Horizon has Triangle Design Motif. Those are the House Matrons.

Redkey, Trocka, and Earthstone, and Jur have a Square Design Motif. Those are the House Patrons. 

Tarko has a Circle Design Motif.

Trug has a Square Design Motif.

Turch has a Triangle Design Motif.

Turok has a Triangle Design Motif.

These are the Rhygear Brothers.

Mathias has a Triangle Motif.

Razus has a Square Motif.

Windchime has a Circle Motif.

These are the Mindblade Siblings.

House Ei has one Child.

Wind has a Triangle Motif.

House Razorblade has one Child. 

Nightraven has a Square Motif.

This is a Square Motif.

This is a Circle Motif.

This is a Triangle Motif.

Characters are defined by their Silhouette.

Reference:

https://www.reddit.com/r/ArtCrit/comments/etdbz9/some_concepts_for_a_character_design_im_doing_for/

One rule I would implement is, when I have a set number of shapes for a character, I do not increase or decrease the number of shapes for that character. I simply resize the shapes as individual Layers for the purposes of showing different perspectives on the Character, and different Poses.

There is also Clothing Design to consider. Making everything skin-tight like it was painted on is just lazy. There should be a consistent design for Clothing too.