So... is Assemble Insert finished or not?
NO, it is not finished.
Why?
The anime finished after the manga:
Anime finished: February 25, 1990
Manga finished: January 01, 1989
... But 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
Tokyo is under siege by Demon Seed, a criminal organization wielding powerful mecha. The police are unable to effectively combat them, leaving the city vulnerable.
However, a young and unlikely hero emerges: Maron Namikaze, a popular idol singer.
Beneath her charming exterior and catchy tunes lies incredible, superhuman strength. Maron takes on the responsibility of defending Tokyo against Demon Seed's robotic threat, becoming the city's last hope.