Ah nice, new player characters for Magic Vigilante!
(Giant infodump incoming. Knowing me, this is a good sign)
Mukurozi and Kei certainly take some getting used to (Mukurozi in particular has a less clear hitbox than the other two, mostly due to the fact that I tend to rapidly tap the movement keys, so most of the time her hitbox looks higher up than it actually is), but they're quite fun once you get used to them.
Mukurozi's super is cool, especially with how you can either use it to keep yourself safe, score additional points, or you can use it more aggressively to shred through the bosses. For the former, it does struggle a bit with high bullet density, and the lack of a time slow can make it more difficult to use, but man is it fun to blitz through the Rival fights in Magic Vigilante Still. Flashback especially gets hard-countered by Mukurozi's super, only really standing a chance in Phase 8, where she stands still and unleashes enough firepower to force you to the left.
Kei's super reminds me of the Laser bomb in Bullet Hell Monday, and I frequently find myself getting way more gems whenever I play as her than as anyone else, likely from clearing lots of bullets with a well-placed laser. She does struggle in the mobbing sections quite a bit, but having strengths and weaknesses makes a character more interesting, so I don't mind.
The Mission mode is a bit repetitive, but the Scenario mode is quite fun, especially with the cute art at the end, and the Magic Vigilante Still her notice falis mode is a neat way to bring the new characters into the original game. Beware, if you play as anyone but Hakuto, it's going to be much more difficult, but that makes sense because the base game was designed with Hakuto's moveset in mind. Even if you decide to play as Hakuto, the reworked lives system puts a new spin on it.
My only real gripes with the game are Mukurozi's unclear hitbox (which can be pretty easily fixed by having the end of her scarf glow like Saba's hairpin in NEHONOBASA) and the short I-frames causing me to sometimes take 2 hits from what feels like one mistake in my positioning (though this may be a skill issue, as the more I play, the less frequently this double hit happens, and I was able to deal with it in AlllCall and Terraria, but then again, those two also have much tankier player characters)
I also find it funny that I immediately started playing the game on Mania, even after you insisted I start with Casual, and it turned out Mania was the difficulty level I was most comfortable with.
Maybe at some point you could include an endless Onslaught mode (or whatever you want to call it), where the game uses sections from the missions, the Scenario mode, and the base game, all in a random order, with frequent boss fights, and the whole point is to see how far you can make it. How long can you last, and how high can you score in that time?
Edit: Just 1cc'd Magic Vigilante Still with all 3 characters
Hakuto had the easiest time, which makes sense because in the base game she's the only player character, so the game was designed with her abilities in mind. She made it through 2nd try.
Kei didn't have it as easy as Hakuto, but she still made it through on her 5th attempt. She mainly struggles in the mobbing sections, and her damage output is low if you're too far away, so you often have to deal with attack patterns you wouldn't normally face with the other two. Pulse, Flashback, and the early mobbing section of 3-1 were particularly tough for her. However, she can score lots of gems with a well-aimed Laser during the boss fights, so she got plenty of extra lives. Due to the nature of the laser, Kei thrives with high bullet density, and therefore Mukorossi was actually the easiest boss in the game for her.
Mukurozi, meanwhile, had a very rough time 1ccing Magic Vigilante Still. Her Super doesn't have as much opportunity to score points as the others', and it's risky to use during the mobbing sections. And due to this lesser scoring potential, you don't get as many extra lives as you would with the other two. Getting hit is fine because you restore to full health in between levels, but if you run out of HP and lose a life, you're in pretty rough shape, unless you're really close to the extend at 10,000 gems. Mukurozi can absolutely breeze through the Rival fights with Mimi, Pulse, and especially Flashback, and the Secret boss is only marginally harder due to the high bullet density. However, the real run killers were the tankier bosses. Uzaki Man was tough because you don't have any extra lives yet (though due to Mukurozi's struggles to get extra lives, even if you did, have an extra life, dying here would warrant a reset anyway), the Big Bunny in 3-1 also frequently ended runs, mostly due to Mukurozi's unclear hitbox, and the Big Big Bunny in Stage 4 was particularly tough, especially its second phase where you have to deal with the extra eyes shooting at you. Normally, when playing as Hakuto, these eyes aren't much of a threat because you can just use your Super to quickly get rid of them, which you're likely to do anyway as the bullets from the eyes would otherwise overwhelm you. Mukurozi doesn't really have that option (Neither did Kei, but she could deal with the higher bullet density and I managed to scrape by with posthumous invincibility), so I just had to burst down the weak point as quickly as I could with a full Super meter from phase 1. And the toughest fight of all for Mukurozi was, ironically, the mirror match. CPU Mukorossi throws so much danmaku your way that now all that Player Mukurozi's Super does is score points. In some phases, it can quickly deplete a life bar, but most of the time it's just a scoring tool, and can maybe protect you from the occasional stray bullet. I've had several runs make it past Big Big Bunny, but die to the mirror match due to either getting hit too much against Big Big Bunny, or Mukorossi herself being such a tough opponent. I even had a run with 2 extra lives going into Stage 4, and I lost that run to the mirror match's final phase because I was too aggressive earlier in the fight.
(Edit: The original and this version were inconsistent with how to romanize Mukurozi's name, so I called the player character Mukurozi, and the final boss Mukorossi)
However, looking back of the footage, Mukurozi's successful run was by far the shortest of the 3
Mukurozi beat the game in ~25 minutes
Hakuto took 35 minutes, though this also includes the opening and ending cutscenes, so exclusing those, she took ~32 minutes
And Kei took 33 minutes
Then I went back to the original and beat it in 42 minutes (I was spamming the Super much more because that version of the game let me, and encouraged me to due to the less forgiving lives system)
So if you wanted to Speedrun this game, Mukurozi is by far the best character for that.
Final note: After 1ccing the original game again, I realized why I was having so many issues with visual pollution in the foreground in this version during the Big Bunny fight in Stage 3-1, but not in the original. The foreground was just as prevalent, but in the original, Hakuto's hitbox appears in front of it so you can still see what's going on. Meanwhile, this version has no visible foreground hitbox, and therefore Hakuto (or whoever else you're playing as) disappears behind the foreground, making downward movement less viable in this version of the fight.
These foreground shenanigans might've also been why Big Bunny was so tough for Mukurozi, and why the early mobbing section in the same level was so tough for Kei, as the bigger bullets obscure your character, too.