Complex sentence: Kakuzu can store up to four spare hearts in animal masks that are sewn to his back, which can be detached during combat situations to shoot elemental blasts at his opponents, and quickly recalled to his body if he needs a replacement heart.
Split into simpler sentences: Kakuzu can store up to four spare hearts in animal masks that are sewn to his back. The masks can be detached during combat situations to shoot elemental blasts at his opponents, and can quickly be recalled to his body if he needs a replacement heart.