6ft, 175 lb like the Paper Warrior? I didn't notice anything about size in the original. Most of these have been 6ft and in the 150-200 lb range.
Speaks Common only since Int is 10?
Tactics: The Keeper prefers to close to melee quickly to make use of its large array of combat options. ???
Looks good, other than a couple of typos:
"The Keeper of the Keysanduses ghost step..."
and
"Once it returns to the frayisit normally fights to the finish."
Thoughts for a description?
I like the mist going through the sandals! And the nazgul-like void. That all sounds great.
Looks very good to me!
Any more possessions to add or "in life" text?
I'm fine with the current possessions of chimes, mithral shirt and spell pouch.
So for the "In life" bit we, as usual, have little to go on.
Presumably he was keen on religion when alive, being a sohei who haunts a shrine.
The Keeper is Neutral Evil, so is there anything we can infer from that? That he wasn't that committed to ideologies?
At 11th level the Keeper was the second highest level of the Swords, with only the 13th level General beating him, so maybe in life he was a bit older than the other swords, perhaps in an "elder statesman" or "semi-retired leader" role?
The original encounter had a swarm of carnivorous beetles hidden in a pit underneath his shrine's altar. They would boil out and attack the PCs if they found the secret catches and moved the altar to access the next part of the adventure. Maybe mention something about carnivorous beetle swarms in the description?
Or we could just leave it simple and not say much so we don't have to invent anything that wasn't in the original adventure. It doesn't even give him a name!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.