[Tempest35]

The Jigen-tou technique does require a lot of energy. Vampires are perfect for learning it because of their own massive energy reserves. It also depends how much the technique is being used and what it's being used for. Even when she was a child, Akua used the Jigen-tou primarily focused around her hands, which along was considered a feat in of itself. Now she can basically phase her entire body out using the technique, which undoubtedly eats up much more energy than just using it around her hands as she likes to do. She was spamming it already when she fought against the Tongs (phasing out of the fire attack, then attacking the Tong family directly, phasing through the wall to get to the gang, fighting Jigen-tou to Jigen-tou against Ling Ling, phasing out just in time of Ling Ling's uzi and 'suicide attack') and then she decided to mimic Fuhai's long range version, which probably nearly drained her completely.

And I think we should wait at least two more chapters before we try and clarify exactly what Tsukune needs to be labeled as of now.