After a wiki binge I can try to answer: it seems that the "Unification Church" is a religious movement popular in Japan and Korea and pressures members into massive donation as well as bringing new members to the church.
The assassin was acting in revenge for his mother's donations to this church ruining their family. Shinzo Abe, the assassinated president, was a high profile member.
So the bill basically sets up a bunch of rules on how donations can be solicited and offers a right of refund if there's anything dodgy about the way the money was donated, or if the victim was deemed to be "brainwashed" into it.
It's only popular because of the publicity gained by assassinating the country's longest serving Prime Minister though. I don't think a pop song would have hit the mark.
It absolutely has affected people in power, as there were more than just him linked to the UC church (which his association with was the reason he was the chosen target) and they were removed from their positions. Thise still in power have cut ties.
It is indeed an uncommon response though.