Izaya's Knife

Izaya uses an switchblade (called a switchblade but could also possibly be a folding knife or assisted opener) in his fights. He was also seen using throwing knifes in the OVA.

History
Izaya used this weapon for the first time in the series when he met and angered Shizuo for the first time to defend himself. Izaya cut Shizuo which caused their antagonism towards each other, driving both to want to kill each other.