Sunbeam is Umagon's book keeper. He has a good relationship with Umagon and is good friends with the other book keepers. He's catchphrase is "Groovy".

Takamine Kiyomaro, a depressed don't-care-about-the-world guy, was suddenly given a little demon named Gash Bell to take care of. Little does he know that Gash is embroiled into an intense fight to see who is the ruler of the demon world. All of the demons have to pick a master on Earth and duke it out with other demons until one survives. Needless to say, Kiyomaro becomes Gash's master, and through their many battles, Kiyomaro learns the importance of friendship and courage. 

Kiyo is a brilliant junior high student whose inflated ego (and tendency to blow the grading curve) has made him a major target for teasing at school. So his father sends him a bizarre birthday present – a strange little boy named Zatch Bell – to help him make friends and reform his bad attitude. Zatch brings with him a mysterious red volume of spells, and Kiyo discovers that Zatch has magic powers that are unleashed by reading from the book! But there are more surprises to come, and Kiyo's destiny is about to change forever! 
 
(Source: Viz Media) 
 
Note: The chapter count includes the volume-exclusive bonus chapter “The Two Queens”.

During the Summer holidays, Gash and gang decide to head for Fuji Mountain for a picnic gathering. There, they encounter a girl with a white magical book. Her name is Kotoha and her book has a message saying that Gash's mother is located a cave in the forest. However, when they eventually found the cave, there was already a blond-haired youth by the name of Wiseman. In order to rescue Wiseman, Gash and the others attempt to proceed into the depths of the cave and stumble upon the entrance to another world. Soon enough, the strongest warrior, the Black Knight, appeared before them. Thinking that Gash was the one who stole the 101st magical book, the Black Knight started to attack them. Gash and Kiyomaro have to find the real criminal in exactly 24 hours, or else they will be stuck in the alternative world forever.

Kafka Sunbeam