Silence

Gintoki and Shouyou didn't need to talk. They understood each other with a single glance, or with just a gesture.

Most of the time, they didn't even need to look at each other, the entire thing just natural. Gintoki letting Shouyou handle some tense situations with villagers because he knew Shouyou would not want him to intervene this time, or Shouyou refraining himself from wrapping a blanket over Gintoki's sleeping form despite his shivering because Gintoki hated to feel restrained by covers. A relationship where words were useless.

Or, Gintoki's relationship with silence, and with Shouyou.