The suspect, 24-year-old Ryūji Kimura (Japanese: 木村 隆二), had previously attempted to run in the July 2022 Upper House election but was blocked due to his age and inability to pay the deposit fee.

[2] Because Hirofumi Kado, a former MP and a Liberal Democratic Party politician, ran for the by-election,[2] Kishida visited Wakayama to support him as the President of the LDP.

On 15 April 2023, Japanese Prime Minister Fumio Kishida was giving a speech in the city of Wakayama in support of a Liberal Democratic Party politician, a candidate running for the by-election,[3] when what was described as a "pipe bomb–like" explosive device was thrown and landed one meter beside him.

"[13] The following day, Kishida vowed to do everything he could possibly do to ensure safety prior to the 49th G7 summit, which will be held in Japan in May 2023.

[18] His lawyers also said that Kimura had become disgruntled when his attempt to run in the 2022 Japanese House of Councillors election was blocked due to his age and inability to pay the deposit fee, and said that he carried out the attack to "try to gain attention in the presence of a famous politician to let the public know his thoughts" after a lawsuit he filed over the election proved unsuccessful.