I saw nobody had reviewed this yet so I thought I would give it my best shot.
Angel is a 1990 released single episode OVA school based hentai, it is focused around a brave and strong headed student called Shizuka who has returned to her home town after many years apart on the hunt for her long lost friend Kosuke, whom she has dreamed and fantasised about for many years.
Unfortunately the school she commences is run by two perverted members of staff, one of whom an overweight middle-aged character called Arihashi is the main antagonist of the story, who gropes female students and abuses
several others in exchange for better grades.
To add to Shizuka's problems, her dream boy is not the brave masculine hero she had imagined, but a immature self-centered, idiotic pervert who is not very likable and fails to improve his behaviour for the duration of the film.
The only other character of note is Madonna, a female teacher in the school who seems to be added in just to make sure at least one of the female characters has large breasts.
In the end the students create a plot in order to catch the the perverted teacher which relies on Kosuke taking photos of Arihashi in the act of abusing a student. However he becomes distracted when he finds Madonna secretly masturbating and wastes all the film of his camera on her.
In the end Airhashi is only stopped by another more masculine male student while Kosuke again fails to be of any help at all.
The art style is pretty much typical of the era it was released, with it being set in a school most the female characters are students and despite not being childish they do not have overly sexualised bodies either. I must say the censorship is very extreme and is the blurriest i have ever seen.
I cannot recommend this anime, it is fairly dated and possibly a little too old to hold the charm of other 90s anime. However if you are interested in abusive teacher stories and 'sex in a tree' scenes, then this may be worth a watch for you.