Paisen is a combat-specialized killing machine. Note: in the Japanese version, Lighter addresses Billy as "paisen" (slang, more playful version of senpai)

Seems that he's able to hide his fangs well in front of you guys.

Whaaa...!?

Huh, that Billy? Really?

So, when he lost Nicole's documents, and that he likes classical music because it makes him sleep well, and all that stuff were just him pretending to be dumb...?

Perhaps he's been a great actor this whole time.

Ehh? Really now!?

We're having a harder time grasping what Billy really is.