There isn’t much difference between all of them.

For Illustrious V.2-4

Trigger Words : Arnes_(Kns), demon girl, multicolored eyes, yellow eyes, orange eyes, slit pupils, red hair, pink hair, long hair, single hair tube, gold hair tube, hair between eyes, sidelocks, facial mark, demon horns, pointy ears

Outfit : bare shoulders, gold collar, multicolored leotard, white panties, brown gloves, elbow gloves, thigh belts, brown boots, thigh boots, high heel boots

Optional : demon tail, red tail, demon wings, red wings

For Illustrious V.2-3

Outfit : bare shoulders, gold collar, multicolored leotard, black leotard, purple leotard, white panties, white chest armor, brown gloves, elbow gloves, thigh belts, brown boots, thigh boots, high heel boots

Optional : demon tail, red tail, demon wings, red wings

For Illustrious V.2-2

Outfit : bare shoulders, gold collar, multicolored leotard, black leotard, white leotard, purple leotard, white panties, white chest armor, brown gloves, elbow gloves, thigh belts, brown boots, thigh boots, high heel boots

Optional : demon tail, red tail, demon wings, red wings, anime coloring, anime screencap

Arnes - Kono Subarashii Sekai ni Bakuen wo! - Illustrious V.2-4