Warning: shit nobody cares about ahead.
Normally when an animate mascot is needed, Ange's would be Mandragora-kun, but I know of one weird time this eye thing was used instead. During JAPAN TOUR 2020 Shout in the Rainbow! Tokyo Revenge Performance, when they were singing 3 倍！Sun Shine！カーニバル！, the video on the stage screen had the eye alongside SebasPiyo and Ban/Ken as Sanbaka's three mascots. It's based on the symbol on the leather clasp of her coat (post #8546482). I can't figure out why and I've never seen it since, but it's cute.

I've only ever found one other person who drew this mysterious thing:

Shou-star