I think this version of the Soul Burial works out better:
I also agree about their Spirit Weapon needing to be... better. I'd go with the Samurai as a basis for what to work with. It still gets Ghost Touch for free, but the Shinigami can imbue it with m0r3 p0w3r. You could charge them a small amount of experience points or gold to get special abilities, but I'm thinking an enhancement bonus ought to come at a level progression (+1 at first, +2 at fourth, +3 at eighth, +4 at twelfth, and +5 at sixteenth).Soul Burial (Su): A Shinigami who is adjacent to an undead or a creature with the Spirit subtype may attempt, as a full-round action, to release the spirit to the heavens. The Shinigami must make a diplomacy check against a DC equal to 10 + the creature's HD + the creature's Wisdom modifier. Hostile creatures receive a +8 bonus on this check, unfriendly creatures receive a +4 bonus on this check, and indifferent creatures receive a +2 bonus on this check. Mindless undead do not get this check; they are simply destroyed, their spirit released to the heavens.
An undead destroyed in this manner can be raised as though it were never undead, provided the spirit is willing.
Methinketh you'd be well-served to change the Undead Slayer to a progression. +2 vs undead at 5th, +4 at 10th, +6 at 15th, +8 at 20th, and so on a la Ranger. Either that, or evil outsiders with the Spirit subtype. Depends on what you want to call Hollows.
I disagree with Innis; unless you want to make a PrC (or say Kido users are multiclass casters), leave the spellcasting progression in. Then again, I don't know ToB maneuvers at all so I'm biased against them to begin with.
... I see nothing wrong with diverging from the source material to give them wings.