The adventurer puts themselves in a position above neutral and focuses their aggressions on increasing with each hit they absorb. Blood loss directly feeds their aggression, so if they take a hit and make a bleeder they will jump a level of aggression. If they take no hits they will take longer to reach the critical mass. In order to stop the acceleration of aggression from gathering the storminess inside, one must perform another action or wait until the Stormgather becomes potentiated enough to release. Each attempt to damage the Stormgatherer while they are active with this Cman will encourage the crux of the potential energy to be reached. If there are not enough physical assaults to encourage the critical mass to be reached then a general time limit will be reached and achieve the same triggering effect. The amount of stored aggression determines the mathematical factoring for the amount of additional damage.

The Stormgathering advantage will be a hike in +AS bonus and a 'free' QStrike effect (on one target only). So the unleashing of the Stormgathering will become a large +AS bonus (unaimable) with a greatly reduced RT. This is to demonstrate that the time it took to gather the violent tempest is reflected by the immediacy of its striking. It is as instant as possible and as powerful as they can make it.

It could work something like this: Rank 1 +10 AS 20 seconds or +20 HP loss or 5 Parried/Defended Attacks (with a formula for each attack coming from a group to have a reduced bracket such as the 2nd attacker counts as .5*, the third .25*1, etc.). Rank 2 +20 AS +30 HP Loss Rank 3 +30 AS +40 HP loss Rank 4 +40 AS +50 HP Loss or 2 Defended Attacks. *Crucial to this Cman would be the absorbing of HP's from the defeated enemy*. So when you kill the beast then you get some of your health back, you 'eat their soul' symbolically and feed off the energy. The heightened adrenaline, victory 'high' and kind of motion you made with the training of Stormgathering when you slaughtered them all feed you enough to give you either a temporary or direct restoration of a good bit of HP's.

It's fairly complicated but imagine it working something like this: The Warrior enters a room with 5 critters. They are all about 12 levels below his. He is level 51 and wears plate. So the Warrior goes into battle there and startles them with a war bellow then goes into Stormgathering mode. His stance bounces up to Forward automatically (he can raise to Advanced or Offensive to factor the acceleration for faster results, changing stance up won't break the Stormgather but it won't be lowered again once it's been raised above Forward by the activation). The adversaries are able to hit him a good bit but nothing over +150s ward AS vs DS and the Plate gives him a huge reduction on top of his redux. He has 4 ranks of Stormgathering. So he begins to wave his claidhmore around in a violent fury, gathering a tempest of energy and daring the enemy to hit them. He takes several blows over about 10 seconds which with the combo of his blood loss, the skillset he has, the rank he has and the number of attempts they made to connect with him but missed.

He gets a +40 (base) AS bonus and eats up about 27 points of health which leaves him with a loss of only -7 HP since they nicked him for 34HP over the time it took to gather the storm. No minor wounds but he got a kill.

In addition to this there is a DS pushdown. The skill needs to be very powerful for the cost and +40 AS isn't always going to even make more of a difference than a good roll. If we won't be able to raise the crit rank directly from the Stormgathering (which would be great if we can combine AS with crit rank but good luck) then I imagine a push-down would be great because the surprise and the timing of the release would be a way to break through defenses. Up to -40 push-down base. So you can wind up with something like your version of Spirit Strike only Stamina based and very ugly compared with the niceness of Spirit circle users.

It's a very brutal and Warriorly kind of thing so I'd limit it to Warriors and maybe Monks.