How is a Prismana Flow weather event triggered in Aniimo?

Both routes put the same weather over the zone, so the difference is timing and cost. A Prismana crystal starts the flow the moment you use it. Energy is the slow road: you build it up in a region, and once enough is released into the zone the flow begins on its own.

That energy is worth building even when no flow is running. The higher a region's stored Prismana energy, the better your chance of a Prismana Aniimo turning up in a group encounter. Prismatic and regional energy moves through tiers, from empty up through very high to full or guaranteed, so you can read where a region stands before you commit an evening to it.

Where the energy comes from

Nurturing is the engine. Nurturing at a Bloom builds the regional energy that spawns Prismana Aniimo, and cultivating an area is what generates Prismana energy there in the first place. Nurturing also helps you capture Prismana Aniimo once they appear, and it lets you change the weather.

Cultivation pays a second dividend while you are at it. Aniimo spawned through cultivation have an increased chance of being Sparkling, and cultivating a region's Branch by infusing Lumin Amber unlocks regional benefits such as the Nurture mechanic, which raises Sparkling encounter chances further.

Turning the weather on yourself

Upgrading a region's bloom branch unlocks the ability to change the weather, and Prismana weather control becomes available at 60 percent completion of the bloom graph. Get a region that far and you stop waiting on a zone to fill.

If you already have the form registered

A consumable Prismana Orb converts an Aniimo into its Prismana variant, but only if that form has been registered before. The flow and the crystal are how you get a Prismana form you have never caught. The Orb is for repeats.

What you are chasing is a variant form with a different visual appearance from the standard Aniimo, and one that can alter elemental typing, occasionally giving a dual typing.

Not settled: How much Prismana energy a zone needs before it flows is not pinned to a stated figure, and it is not settled whether the energy build and the crystal are two separate triggers or two descriptions of the same one. Nurturing's standing is open in the same way: it is given as the main route to Prismana Aniimo and also as one route among several.