A couple people have said this and severe does not mean death, It means really really bad. If I say to a doctor the patient has severe bleeding on his right arm, that does not mean the patient is dead , or that his right arm is dead. It does mean that his right arm needs repaired beyond that of normal means. Also twilight scythe has death already on it.
To me it sounds like an attack that ignore's the mobs defense(100% would be sever but I doubt SE would be that cool), or most likely knowing SE a 100% critical hit damage bonus, if they could program it easily probably over the 100%, but I doubt since it took aegis forever to be able to go over 50% cap.