It takes a moment, when the merman taps on him, for Ginko to process what he just said, and what he presumably meant by it. Then his face lights up a little, because this sure seems like progress, which is pretty damn exciting??

"Oh! Uh, J... Joh-kah?" His pronunciation is a little bit of a mess, but he tried. After a moment's hesitation, he taps the hand over the merman's chest, not quite willing to just... put his hands on his chest. Not quite at that comfort level yet.