Before the series begins, Kazuki throws it after Haruka's incident. In Episode 3, Haruka manages to take it back and gives it to Enta. During Haruka's rescue, it is given back to Kazuki. After this event, Kazuki is seen wearing after that.
By Episode 11, the miçanga has become the symbol of the connection between our three protagonists. It gets cut by a bullet that Toi shot to his younger self. But Kazuki reconnects it. The trio manages to give it to a 10 year-old Kazuki.
In the Epilogue, it is still attached to Kazuki's foot even after 3 years.
Enta's red miçanga appears briefly in Episode 1. It hints at Enta's feelings for Kazuki.
In Episode 2, Enta and Toi mix up their boxes. Toi gives it back to him at the end of the episode.
It makes its last appearance in Episode 3, being attached to Otone's foot by accident. Once Enta got it back, it ends up being stole by a mouse.