In Bleach, Ichigo Kurosaki is the hero, a high school student turned Soul Reaper, complete with a powerful Zanpakuto. Ichigo's unusual body grants him many abilities, but he's not the only one with a quirky set of talents. Reaper Captain Soi Fon is a trained assassin who has total mastery over her fearsome Zanpakuto, Suzumebachi.
Primarily, Captain Soi Fon takes after her mentor, the noblewoman Yoruichi Shihoin, by favoring speed, melee attacks and trickery to take down her enemies. The Shunko technique, a combination of martial arts and kido, is a good example of that. But if the enemy is very strong, then it's time for Suzumebachi.
Soi Fon's Shikai Mode, the Stinging Butterfly
Soi Fon's Zanpakuto does not take the form of a katana like most others, such as Captain Tosen's Suzumushi or Captain Kuchiki's Senbonzakura. Instead, Suzumebachi takes the form of a short sword, light and maneuverable like Soi Fon herself. It's a blade fit for an assassin, and its power only increases when Soi Fon decides to activate its Shikai. Soi Fon declares "sting all enemies to death, Suzumebachi," and her Zanpakuto transforms at once. Its Shikai form is among the smallest out there, abandoned its sword form entirely to turn into an armored glove of sorts. It is made of gold and black metal, and the most important feature is its long stinger on Soi Fon's right middle finger. All of Suzumebachi's power is focused on that stinger.
If Soi Fon stings an enemy, even a powerful Hollow or a fellow Soul Reaper, the target will have a distinct butterfly pattern marked where Suzumebachi touched them. This mark doesn't do anything on its own, but if Soi Fon stings that same place twice, the target will drop dead at once, no matter how tough they are and no matter what kind of armor or spiritual pressure they have. During the battle for the fake Karakura Town, Soi Fon used this power on an Arrancar soldier named Ggio Vega, and she was able to stab Ggio once each from the front and back. The two stings touched inside Ggio's body, satisfying Suzumebachi's "double sting" condition. It should also be noted that the butterfly marks will not vanish until Soi Fon wills it, and she can create several at once on her target.
Suzumebachi's Bankai Mode, Jakuho Raikoben
Captain Soi Fon only very rarely uses her Bankai, since it completely contradicts her stealthy style of fighting. Its name is Jakuho Raikoben, and it takes the form of a massive, arm-mounted missile launcher. Once this Bankai is released, Suzumebachi encases Soi Fon's right arm, complete with a face guard with a few slits for aiming and protecting her face. In addition, Soi Fon tends to use metallic cables to tether herself to nearby structures before firing, so this flashy Bankai's power won't blow her away. When Jakuho Raikoben fires, it looses a single, powerful missile of spirit energy, creating a lot of noise and light as it goes. This Bankai can be fired once without consequence, but if Soi Fon fires it twice in one day, it exhausts her.
Soi Fon used this Bankai while fighting Barragan Luisenbarn with Hachigen Ushoda, firing its destructive energy into a kido castle that trapped Barragan inside. She fired twice, in fact, and greatly injured one of the most powerful Arrancars alive. Later, she used it again when fighting the Sternritter called BG9, injuring it and forcing it to retreat. BG9 had once stolen Jakuho Raikoben, but not for long.