Samejima is a notorious arms dealer who smuggles cheap weapons in from China and re-sells them in Tokyo. In the past, he'd sold his guns to many criminal groups, though his biggest clients were yakuza families. Eventually, however, he was approached by the leaders of the Reapers, who offered to pay him to sell guns to them exclusively. The offer was so lucrative that he agreed and became the vigilante group's weapons distributor.
After he joins forces with Ibuki and the Honest Living Association, Kiryu is sent to find Samejima's base of operations and stop his gun sales to the Reapers.
Kiryu eventually track down the merchant to an office building in Senryo Avenue. Upon announcing that he is a member of the HLA, Samejima correctly deduces that Kiryu is there to stop his gun distribution to the Reapers and orders his men to kill him. Despite the fact that Samejima's men are armed with guns, Kiryu manages to defeat them all. Irritated, Samejima draws a submachine gun and attacks Kiryu himself, but he too is beaten in battle.
After the fight is over, Kiryu threatens Samejima into no longer selling guns to the Reapers, but he is unable to persuade the gun runner to give up the leaders' identity, since Samejima claims that he "guards his clients' privacy". As a reward for stopping Samejima's gun running operation, Kiryu is paid 140,000 yen.