Project ARMS Vol 7

From the VIZ Media edition

Ryo, Hayato, Takeshi, and Kei are Arms - kids implanted with nanotech limb enhancements that cause them to transform into grotesquely deformed and out of control superweapons. In a desperate attempt to dispose of a neutron bomb on the verge of exploding, something is triggered within Takeshi's body that causes him to transform into his ultimate form...

Source: Anime News Network Encyclopedia