I may be wrong, but it's my understanding that a quick, random sketch is 'rakuga', and a 'rakugaki' is someone who does them. I think the... I guess the correct term is 'noun' form, 'rakugaki', is a pun on 'gaki', which means 'brat'.
This is AMAZING!! It really caught my eye! I'm telling you, you really have the talent to make it BIG!! Your artwork...has such a UNIQUE style! I luv it...I'm currently trying to find my own unique style cuz I think thatz what makes an artist truely beautiful, and you really do shine.