I would use that sans the immunity to magic and no need for food/water.
The variable for upgrading the scythe would probably be souls either a) sent to the afterlife (standard Shinigami) or b) devoured by the scythe (Soul Eater). And I'd probably make it every 10 or 100 souls, since it's the Shinigami's job.
Light step sounds good as well though it's made moot by the levitation, and the spirit sense would be part of the passives gained every other level.
The drain attack sounds good though more of an application of the Reaper Scythe than as a standard unarmed attack.