The Mainichi reported on Tuesday that a bomb threat was delivered to the Kai Intellectual Property Law Office in Sakura, Chiba Prefecture, in the early morning of May 16. This news came after YouTuber Yuzuha registered the trademark "Yukkuri Chabangeki" on May 15, which refers to fan-made disembodied head versions of ZUN's Touhou Project characters.

Yuzuha first stated on Twitter that a licensing agreement will cost fans 100,000 yen (about US$770). She eventually recanted her declaration, but maintained her trademark rights. Fans chastised Yuzuha since, as of October 2020, the staff of YouTube channel Touhou Danmaku Kagura had confirmed with the ASCII art creator, the artist, and ZUN that "Yukkuri Chabangeki" could be freely used by anyone.

In September 2021, Yuzuha filed a trademark application. On Yuzuha's behalf, the law firm that received the threat applied for trademark registration. As a result, a number of fans have contacted the law firm and launched a petition to oppose Yuzuha's trademark. Following that, a person claiming to be connected in the Yuzuha case sent a message to a web portal near the law firm's location that read, "Multiple bombs have been put there." Around 3 p.m., they'll go off." On May 16, about 2:00 p.m., the Yamaman Yukarigaoka Line and the community Koala Bus were temporarily discontinued. "We are sorry for the inconvenience caused by not knowing that the trademark has been registered and, loved by everyone." the law firm said on its website the same day.