The fan's reason for this is:
"Prime Minister Abe is a Miku Hatsune fan. Japan will turn into an anime kingdom at this rate".
This reasoning is hard to comprehend, but it seemed like this person was serious. She tweeted her feelings in the morning of the 23rd, the day of her alleged execution.
* Early morning of the 23rd:
"Today is D-day... I'm seriously getting a bit nervous... But I'm doing this for the sake of Japan."
"VS Arashi airs today...I have to execute this until that time comes..."
A lot of netizens were quick to report her to the authorities, and she tweeted that she's given up her plan by 9 in the morning.
"When I told Satoshi about my plan, he told me to stop... I don't want to make Satoshi sad so I won't set it on fire anymore... Everyone in Japan, sorry..."
It seems that the plan has fallen through, but these tweets are still terrorist threats, aimed at Prime Minister Abe at that, and may lead to grave charges.