Zabimaru

Zabimaru (蛇尾丸, Snake Tail): Zabimaru's sealed form resembles a typical katana. It has a rectangular bronze tsuba with a jagged design, and a red handle and sheath.

Renji shikai Zabimaru's Shikai state. Shikai: Zabimaru's Shikai command is "Howl" (咆えろ, hoero; "Roar" in the English dub). In its Shikai, Zabimaru transforms into an even longer 6-part segmented blade; each segment is wider than the one preceding it from the hilt, with 2 pick-like protrusions on the front and back of each segment, with the ones on the front much longer than the ones on the back. Zabimaru's segments can grow in number almost without limit. The segments are connected by a stretchable thread, making Zabimaru more useful as a whip than an actual sword, however, it can serve as a regular sword just as easily, thanks to Renji's swordsmanship. Zabimaru's guard and handle remain the same in its Shikai release.While Zabimaru can be stretched to incredible lengths in its whip form, Renji has a limit of three consecutive attacks before having to bring the segments of Zabimaru back together for recovery - leaving him fairly vulnerable. To make up for this, Renji usually relies on Shunpo to evade attacks as he retrieves Zabimaru's segments.Renji's Shikai, while durable to an extent, can ultimately sustain serious damage the longer the fight drags on. While it can withstand dangerously prolonged combat, it has limits in enduring high-level attacks that are conducted by either the enemy or by Renji himself. Because of these many drawbacks, Renji states that out of all the Zanpakutō wielded by the lieutenants, Zabimaru is the most difficult to master.