Jerma being in Tsubame's place was something that was decided more or less by consensus; the first bit of fanart for it only focused on Vinny and Joel, and after bringing up who Tsubame would be everyone more or less agreed Jerma would be the best fit given his similar dynamic with the two.

Vinny brought this up during the art segment but I do really love how Jerma has essentially been integrated into VineSauce from the perspective of the viewers. Vinny always speaks positively of him like a friend whenever he comes up and Joel's been interacting with him a lot lately too so that probably helps.