This is Ichika's collar from the visual novel Collar x malice!

Supplies

I used Tinkercad!

Step 1: Making the Base

Start out with a circle of your preferred size for the neck and thickness

Step 2:

I made lines in the shape of an "x"and made them thin to divide the ring into sections

Step 3:

I used multiple hole shapes to delete 3 of the sections so I just had one (because they all had to be the same anyway)

Step 4:

I made a pill-shaped preset with half circles and a cylinder to make the indents on the sides, and the notches

Step 5:

Made the "screws" by lining up a spiral to where I wanted the pieces to interlock and duplicating with one of them being a hole shape I grouped with the collar

Step 6: Making the Charm

I just placed circles where the main curves needed to be and used the letter "s" which I cropped to fill in the rest

Step 7:

I made the ridges on the red part just by duplicating multiple flat vertical lines that were holes and grouped it to a circle, with the whole cat being made with the basic shapes except the tail which was a cropped letter "s" stretched

Step 8: Assembly

Duplicate the 1/4 part of the base and line it up to make the collar again, and use the basic shapes to create the design on the front (use the align tool to help)