Chocola is mostly a normal, everyday bright young middle-school student who just wants to fit in. Unfortunately as a vampire and the daughter of the famous vampire in history, Count Dracula, that's a lot easier said than done.
Gratin is one of Tezuka's Star crooks who seems more to have simply fallen in with a rough crowd due to his odd appearance. He was likely looking for acceptance amongst his peer group - specifically Kao Sekken and Afill who often appear alongside him. He acts tough to hide his own insecurities and is often cast in the role of a thug, a henchman, or some other sort of servant.
Dr. Fooler is another of Tezuka's mad scientists. Childish, both in his appearance and in his behavior, he is nosy and pushy and often worms his way into business he should not be part of, or pushes forward ill-conceived scientific projects against the better judgment of wiser scientists.
Types of Tezuka Manga
Ongoing Serial: a series of episodes, published over a span of weeks/months/years where the story plot is connected from chapter to chapter and must be read in chronological order for it to be understood properly.
Chapter Serial: a series of episodes, published over a span of weeks/months/years where the story plot is self-contained to a single chapter. There may be an overarching plot, but the stories can generally be read in any order and be understood
Book: an all-in-one self contained story published as a one-off.
Supplement: an an all-in-one self contained story published as a stand-alone supplement to a regular weekly/monthly periodical.
Short Story: an all-in-one, self contained story that was published in a regular weekly/monthly periodical
Anthology: a collection of all-in-one, self contained stories that were published in a regular weekly/monthly periodical but are generally grouped together.