"Sucking on your finger gave me an idea..." (slightly r18)

  For a spiritual realm cultivator like Veila, spiritual energy was everything.

For as long as she maintained a healthy level of spiritual energy inside of her, she could easily go for extended periods of time without sleeping, eating, drinking or even breathing. 

Obviously, having mana in one's body only allowed one to cheat nature, not to alter it. And while a spiritual realm cultivator could starve himself out for months, the burden of maintaining his body through spiritual energy alone would only continue to grow greater and greater with each passing day without a meal. 

Spiritual energy was ultimately just a bonus, a supporting feature rather than a complete alternation of one's body. 

That's why, when Theo started to pump his excessive mana directly into Veila's body, the change at which her wounds started to heal became apparent to anyone who would bother to look.