"The ability to manipulate the unconscious" means being able to have your actions go as unnoticed as a pebble on the roadside, even when in someone's direct line of sight
"Pebble" here stated in a way that would be pronounced as "koishi".
The 14th of May is
Komeiji Koishi's Day!
The date is a pun:
Koishi → ko(→go; 5) i(1) shi(4)Well, guess that means you're also close to this side then
This side meant to be something like "being part of a group that's apart from normal society" or otherwise "belonging to another world" (such as a criminal underworld or what have you). The implication is that, whatever it is you are or you're doing, you can't be considered "normal" by societal standards. Reckon it's meant to sound somewhat edgy most of the time.
