It is overtly stated in the second half of the anime that the Heroe cannot die, since their fairies protect them.
Togo attempted suicide in every way possible to her, even by carbon monoxide asphyxiation and poisioning, and the fairies protected her every time.
Even when battling the Vectors, the worst they get is a bashing against the fairies' shield and powering down.
In the prequel novel there seems to be a character by the name of Minowa Gin that died.
What were the circumstances of her death?