Since I haven't used them for a long time, I'll make some head-canons about them and their differences.
HEADCANONS/FACTS:
-Fuzzy is about 18 years old while Fizzy is 19. That makes Fizzy 1 year older than Fuzzy.
-Fuzzy's real name is Fuzzel. He doesn't mind being called "Fuzzy" by almost everyone.
-Fizzy's real name is "Fumio" but he doesn't like his own name so he goes by "Fizzy"
-Fuzzy has a strong dislike of violence and gore, but Fuzzy can force to kill someone if he felt panic or scared about dying.
-However, Fizzy is aggressive and he uses violence to solve everything. He won't hesitate to kill someone if he felt like he needed to do it.
-Fuzzy sees Fizzy as a brother because he looks up to him and Fizzy is his only friend that almost shared the "zzy" ending in their name and starts with an "F" as their first initial.
-Fizzy secretly likes Fuzzy as a friend. He pretended to be mean to Fuzzy, even he didn't intend to. Fizzy see Fuzzy as a soft and open friend. It makes Fizzy trust in Fuzzy a lot more than anyone.
-Fuzzy is a "weeb" fan. He mostly watches anime before he goes to sleep and talks about anime with someone who is a strong interest in anime.
-Fizzy is a fan of dark and emo stuff. He is also into literature.