Kizuna

Kizuna is a game mechanic found in Live On Stage where characters level up bonds together. This only works in Produce mode. By partnering up two characters, they will gain +5 bond (+2 in Event Produce.)

You need 30 bond to level up the kizuna between two characters to level 2, and 70 to level it up to 3.

Starting level 2, during a Live those two characters might be able to perform a Kizuna Performance. Those two idols will then say each other's name and perform their unique pose. If they are level 3, a unique line between those two will also appear.