Aozora's appearence was slightly inspired by the player's character from
Famicom Jump: Hero Retsuden (as shown below, bottom right)
...While Paku-Chan and Ball-Kun were based on a combination of Bomberman and Terrance & Phillip. Very little ideas for Satoru came from a few things, the most major of them being the main character from the flash series of video games known as
Hostility 2112 (at least, that's what I think l it's called), while a few of Zik's ideas came from Roger Sasuke from
Shikigami no Shiro and "Zach" Braun from the
Sky High film. Sakaki was inspired by a number of gothic-esque characters, mostly Magenta from (once again)
Sky High and (for the long hair) Grolla Seyfarth from
Rosenkreuzstilette.