Seiichirou Kitano is a naive and kind boy with the heart of an angel and the face of a devil. Upon entering his new school he is presumed to be a villainous heroin addict, and unwittingly becomes the leader of the schools thugs, all thanks to his frightening face. His new "friends" have great expectations of him, seeing him as a frightful demon. Kitano himself on the other hand, loathes violence and is blissfully unaware of the situation he is in...
If you enjoy either Ochi Nigosu or Angel Densetsu, I'm certain you'll enjoy the other. Both have a young 'evil-looking' protagonist, who are a most often misunderstood based on their looks. They're both stories of the hardships they face and their journey to become 'better people' in the eyes of society.
The main charachters themselves are very similar in a way. They both appear to be sinister on the outside but are actually nicer than they look and mean well.
The storys both revolve around them being misunderstood by others but slowly gaining understanding and friends.
Both series' are about a guy who has the face of a demon trying to be good and right in the world. Misunderstandings abound and the driving force of each series along with that whole demon face thing. And they're funny to boot, that's school comedies for you.
Both manga have a male deliquent protagonist with a best friend that contrasts their personality. The difference being is that the main character of Ocha Nigosu is a demonic looking delinquent trying to become a 'better person', whereas Kyou Kara Ore Wa!! features a boy who is doing his best to become the dirtiest and most evil thug around. Nevertheless, they are both hilarious and feature similar comedy and action.
Both manga's are from the same artist. So the art and humor are quite similar. Wich is actually the biggest thing this manga's have in common and also the thing that makes both manga's fun to read.
The stories both contain humor and delinquints. The big differents is that one of them (Ocha Nigosu) wants to be good and the other (Kyou kara ore wa) wants to be bad. Ocha Nigosu has a better story and is a bit more serious.
A naïve, slightly doltish, violent delinquent with a heart of gold is a rather clichéed character, but sometimes they work. Masaya Funebashi of Ocha Nigosu and Genzo Soga of Tenshi na Konamaiki have a lot in common, and so do the two mangas (not surprising, as the art and story is by the same author). Granted, Soga is not the main character of Tenshi na Konamaiki, but he plays an important rôle. If you like to read about one of these guys, you'll like the other.