Soulmate Au|You are born with a simple tattoo on your hand or wrist with a simple tattoo on your hand like a dot or a straight tatoo becomes more detailed,intricite and large the closer you are to your soulmate(in a literal sense)

Kazuichi noticed that his hand and forearm is covered by a pattern whenever he's with Fuyuhiko,Fuyuhiko didn't notice until when he was fixing his sleeve while Kazuichi was walking away he saw the pattern fading.