To those wondering about how the suicide loli managed to fight with such a limited ability.
Many of you here have overlooked a single detail; she's the [LAST LINE OF DEFENSE].
The idea is simple; the other guardians should have whittled away all but the strongest enemies in the event an attack actually makes it that far.
With her ability she can then sacrifice herself to either kill the last great challenger or at least the greater threat to the maou among those that remain.
No matter what no one who challenges the Maou will reach her without losing someone important from their team.