Assassin assigned to assassinate the unkillable (A hxh and assclass crossover)

Before Killua Zoldyck had escaped his brother's chains, killua was assigned a special mission but the government. To join class 3-E on their mission to assassinate their teacher, the one who oblidarated more than half of the moon and caused it be forever crescent, Korosensei. The unkillable yellow octopus who can move at the speed of Mach 20, breaking the sound barrier as he soars through the sky, is the target of this operation.