Looks like Heiro's already having fun with the tickling fad and it's only his first time too!
If you're wondering what those weird inky black Unown are then fair enough, I'll tell you.
The shadowy Unown are spirits/ghosts of the Unown denizens that once resided in the Ruins of Alph. Even after death, they have a rule of passively welcoming and interacting with the living of their own kind, outsider or not.
So when Heiro visited the Ruins, the spirits welcomed and greeted him with respect as he was one of them.
Sadly for Melody however... Well, the spirits weren't too pleased with an unrecognised and unrelated species intruding their resting place so Heiro offered to punish her for them.