So... is Madonna finished or not?
NO, it is not finished.
Why?
The anime finished before the manga:
Anime finished: June 23, 1989
Manga finished: January 01, 1992
MangaUpdates contains information about the anime adaptation and indicates that it is incomplete.
Watching Order (by release date)
Here you have all the anime relations we detected ordered by release date, so you can see the reason for this status in context and also use it as watching order.
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Synopsis
Madonna centers around Mako, a new, attractive teacher at Gyunabe High School.
She intends to educate her students, but faces unexpected challenges from a class of unruly students, particularly their mischievous leader, Obayashi, who is determined to see her underwear.
Mako struggles to maintain order and her dignity as the students constantly try to embarrass her.
Adding to her troubles, the principal assigns her the role of rugby coach, despite her lack of experience, further complicating her life at Gyunabe High.
The anime explores Mako's attempts to survive and succeed in this chaotic environment, battling her students' antics and her unconventional coaching assignment.