If there's one thing I've learned from watching plot power discussions on Board 8, it's that they actually can be reasonably objective. While the average RPG character doesn't have much in the way of quantitative plot power, the average, say, Marvel character will usually have a database on how much they can lift, how much they can blow up using their mind, and so forth:
What I'm going to try to do in this topic is get a ballpark estimate for Touhou characters. The unit of measurement I will be using is Kilograms. Before anyone objects "but you can't account for speed with kilograms"--on the one hand, not really, but on the other hand strength to a large degree determines speed; to use more comic examples, the Hulk can leap 2 miles in a couple seconds. Any of those "near lightspeed" characters like the Flash needs insane strength to accelerate from 0 to 1,000,000,000 km/h (easily enough force there to lift up a skyscraper).
So...anyway, on to actual Touhou stuff. (Spoiler warning I guess)
OFFENCELet's start with the outlier from Highly Responsive to Prayers:
(B-route)
(A-route)
This is an explosion that looks like it could, say, blow up the moon pretty easily (about 10^22 kg). That said, I really don't know what's going on in that scene. These are two of the bad endings, and my best guess is that it's Reimu saying "what does this button do?" *kaboom* "Bad Ending #1: try to win without continuing so that you don't blow yourself up". Furthermore, if Reimu could blow up a moon-sized object with relative ease, then the plot of Imperishable Night doesn't make a whole lot of sense (why don't they just blow up the fake moon?) Moon-sized explosions and creating a fake moon are abilities that seem to be used only outside of combat, at any rate.
So...alright, Master Spark:
Juding by the picture...it's about 12x the height of Marissa (witch hat included). She's probably like...4 feet tall, 5 feet with the hat. That makes Spark about 60 feet in diameter (Actually I'll say 50 just because it's a round number). In manga, Master Spark has been shown to blow through the walls of buildings. I could definitely see it blowing through multiple walls, or multiple floors if it was aimed vertically. Okay, so how big of a building could it incinerate?
Hmm...just because I have the numbers handy...the World Trade Center was 208 feet x 208 feet x 1362 feet and 5x10^8 kg. This is too large in every dimension probably, but if we scaled this down by a factor of 4 in every dimension we'd get 52 x 52 x 340--within reasonable dimensions for Master Spark. The weight of this smaller skyscraper would be (5x10^8)/4/4/4 kg = 8x10^6 kg.
DEFENCEWell...canonically pretty much every character in the series has tanked a Master Spark and kept on fighting so that's 8x10^6 kg. Granted, the characters are also small enough that they don't get hit by the entire energy blast of Master Spark.
Alright, so I looked to Perfect Cherry Blossom, Sakuya A against a character of not particularly special durability (Youmu). SakA fires out 30 knife waves, roughly 5 times per second, so 150 knives per second.
Youmu has 4 spellcards and 4 openers, which take SakB approximately 20 seconds each to kill (time-slowing accounted for). This means that Youmu tanks approximately 20,000 Knives moving at...based on in-game I'd estimate 150 km/h (100 mi/h). The knives aren't generic, either--Sakuya tells us they're made of silver. So...okay, 150 km/h silver knife, that's enough to kill, say, a 100 kg human. So... 20,000 knives x 100 kg = 2x10^6 kg. (Of course, this doesn't kill Youmu or anything; she comes back for another round in stage 6). Surprisingly within the same order of magnitude as Master Spark.
For another example, Utsuho is pretty content chilling at the center of a nuclear reaction:
(She's in there somewhere).
Now, nuclear weapons vary greatly, but the standard nuclear bomb seems to create a blast of approximately 2x10^7 kg of TNT. 10^7 is a little higher than other numbers we've seen for durability, but on the other hand Utsuho is canonically very durable.
So...those are all the semi-functional examples I could think of at the moment. A lot of the other stuff is just "whee, magic" which doesn't translate into a clear kg value or anything. Still, it's surprising how all the ones drawn from in-game fights come out to a very similar order of magnitude.