How does Lightning Blade Storm work?

EP is both the fuel and the timer. You do not choose when the slashes stop, so the length of the whole thing is decided before you ever press the button, by how much EP Fulmintis has in the tank. Open with a full bar and you get a long run. Open with a sliver and the dash happens, a few slashes land, and it is over.

That makes EP management the real skill here rather than aim. The drain keeps going for as long as Fulmintis is attacking, so a committed Blade Storm empties the bar and leaves nothing behind it. Plan what comes after.

Element matchups significantly change combat performance, so the same number of slashes into two different targets is not the same damage. Pick who you dash at.

The final spinning slash is the payoff

Every three consecutive hits you land during the ability raise the damage of the closing spinning slash by 100%. The slashes in the middle are not filler. They are loading the finisher.

So you want the target still in range and still being hit, not staggering out of reach halfway through. A run of clean connected hits is worth far more than the same hit count spread across a target that keeps slipping the chain.

Calling it in Command mode

In Command mode the Pathfinder stays on the field and issues abilities while the Aniimo fight on their own. Blade Storm is one of the things you order rather than something you steer through, so the dash and the whole slash sequence resolve under automatic control once the call goes out. Your input is the timing of that call and the state of the EP bar when you make it.

Not settled: How a broken streak is treated is not settled. The bonus counts in groups of three consecutive hits landed, but whether a missed hit resets the count or only pauses it is unclear.