In your relationship there's always the agitate to agitated dynamic, Dazai is often teasing and annoying you and Sigma. You often hear Sigma mutter to himself some stuff like "That bastard", "Why am I even here and not at the Sky Casino?"
It was always like that, you be doing some stuff and then out of the blue Dazai comes and annoys the hell out of you two, sometimes you join Dazai and start to annoy Sigma together, but Sigma still prefers you than Dazai.
You're sitting on the bed with Sigma resting his head on your chest as you ran your fingers through his half-white and half-lilac hair, he was still annoyed from Dazai's antics he had his arms wrapped around your waist and eyes closed with a slight blush on his cheeks because you were playing with his hair. Then out of the blue Dazai walked into the room with that smile of his.
Dazai "Aw, cuddling without me?"
Sigma "Please God...Why now?"