After defeating rizevim issei and the whole factions started attacking Trihexa but they couldn't defeating him
Trihexa; just give up already i am powerful
sirzechs; you not powerful
azazel; i have a plan but i think you won't like it
Michael; let's do it
azazel; we have to Sealed our self
sirzechs; ok let's do it
the three factions try to Sealed them self and they did it
Trihexa; no i will be back some day
issei; bye beast monster
Trihexa; no
issei; well bye teacher i will miss you
azazel; i know but i will be inside forever
issei; ok i will meet you some day
azazel; yea
chapter- 18 after the war