Context: a tentacle monster destroys the moon and will destroy the Earth next year unless his class of assassin students manage to kill him before then.
koroseru to ii desu nee 殺せるといいですねぇ
If able to kill: good.
It would be good if you managed to kill me, don't you think?
koroseru 殺せる
Able to kill.
(potential form of...)
korosu 殺す
To kill.
sotsugyou made ni 卒業までに
Until graduation. (i.e. within one year.)
