Another trauma signature weakness. Looking at the two elements, the effect and the discard condition, we get:
The effect: It drains Akachi's charges by forcing her to exhaust spells to build up 4 charges on this card before the end of the scenario, or face a physical trauma. Since Akachi usually has plans for those charges, this is a bad situation. While her Health is better than Roland's Sanity, physical trauma is still no joke and can end the scenario, especially since, like the whole suite of trauma weaknesses, if Akachi is defeated before getting the requisite charges on this card, she gets bonus trauma! On the upside, other investigators in her location can move charges as well, although it's not that common to have other spells with charges floating around. The largest problem with mitigation is that you want cheap spells with #+ charges, and they pretty much all take up Arcane slots that you already have plans for. You could use Sign Magick or Familiar Spirit to get more Arcane slots, but that is increasing the cost overall. Useful, low-cost spells include Alchemical Transmutation, Clarity of Mind, Healing Words, Mists of R'lyeh, and Song of the Dead, and Akachi's ability makes sure they have plenty of charges. One significant advantage to this card over other trauma weaknesses is that you will generally have two spells out, and Akachi can exhaust both of them in any free triggered ability window, allowing her to fill this weakness in two turns, drastically reducing the danger of a very late game draw. Now that Brand of Cthugha (4) exists, it would be pretty easy to siphon some of those 9 charges toward this, assuming you weren't the primary killer on your team.
The discard condition: None, but, if you get 4 charges on this card, you disable it (and it does not get discarded).
All in all, this is an average signature weakness.