The blast, occurring at around 8:50 p.m., sent chunks of metal into a wall of the compound and around the immediate area. Four cars in the parking garage and a sliding shutter sustained exterior damage.
Two gang members were inside the two-floor reinforced concrete structure, which is owned by the Dojin-kai’s 39-year-old chairman, but there were no reported injuries.
Investigators suspect the incident is the result of an ongoing dispute the gang has with the Kyushu Seido-kai criminal syndicate.
In August, the Kyushu Seido-kai was believed to be involved in a similar grenade attack on the Dojin-kai compound. The next month, a building in Tsubukuimamachi owned by the former wife of an upper member of the Kyushu Seido-kai was hit by a Molotov cocktail.
The Kyushu Seido-kai began in 2006 as an offshoot of the Dojin-kai following the resignation of longtime Dojin-kai boss Seijiro Matsuo. In Fukuoka, Saga, and Kumamoto prefectures, the gangs have a history of engaging in violent incidents.
In November 2007, Fumio Imada, a Dojin-kai member, was arrested for the shooting death of a male patient in a hospital room in Saga Prefecture. The previous occupant of the room was a member of the Kyushu Seido-kai.
The feud has been intensifying in the last year. The Dojin-kai is believed to have been behind multiple murders of Kyushu Seido-kai gangsters: An explosion killed one boss and his brother inside a car in Omuta in April 2011, and, that same month, a member was stabbed to death in Ogi, Saga Prefecture.