Reaper speculation thread

[Arkdra]

Here is my 2 cents:

Using the pet has a hefty MP cost (voidsents feed of aether after all, and it's likely part of the pact to summon it). "Feeding" it builds up a ressouce/gauge to trigger the fusion.
You have to use your scythe to "reap" MP from ennemies and keep yours up as much as possible to keep the pet fed and beeing able to call upon it.

MP management would make sense I suppose since the other darkness themed job does it. And the lore bits you mentioned line up too.