Blarblade or blarraven for shigure (PA)?

You really don't need an offensive Dancer because his primary goal is to provide dance support, so I would not recommend -Blade Tomes. I've seen a good amount of people use the Blarraven + Triangle Adept so that he can be a dedicated Colorless and Red check, and it's a nice utility to have for the team. Between the two, I think that the -Raven Tome is the better choice.

Personally, I just stuck with his default weapon since I never needed a Colorless check nor did I ever intend to put him into range of anyone in the first place. (Also, I didn't want to spend 20K feathers for a fully upgraded Blarraven.)

I agree with Master NaCl, dancers are just there to support the team, especially the PA dancers. People do put RavenTome on him but I think it's a waste. Imo, RavenTome+TA is only good on Green Tome units. They can check the infamous Reinhardt and B!Lyn combo. I have a PA Shigure and I turned him into a bit of an offensive unit with SB and Darting Blow. Might give him Fury and WoM. His default tome is great in some scenarios.

You could go Blarserpent or Blarowl, the latter notably has a way of increasing Shigure's Spd besides a refine.

Sometimes "the best defense is a good offense" applies to the dancer units, but Shigure just has such an awkward stat distribution with a truly middling Spd stat.

I have a +Atk -HP version, and I went with Bladetome. I built him with DB3, Geyser Dance, Spur Def/Res and Spur Def. His main role isn't to do damage, but with the boon, a Bladetome and DB3 he can do clean-up when necessary (which is hopefully never, but still). I think I'd go that over Raven, as the premier colorless units will probably still kick his butt anyways.