Complex sentence: Luppi temporarily replaces Grimmjow Jaggerjack as the 6th Espada in Sōsuke Aizen's army of arrancar when Grimmjow is disabled by the loss of his arm, but later regains his position by killing Luppi after his arm is restored.
Split into simpler sentences: Luppi temporarily replaces Grimmjow Jaggerjack as the 6th Espada in Sōsuke Aizen's army of arrancar when Grimmjow is disabled by the loss of his arm. Grimmjow later regains his position by killing Luppi after his arm is restored.