Hey, Sorry for the hug delay, let's get to work!
Kantan
00:06:344 (4,5,6) - This does sound a little complex, I understand if you don't change, however
00:11:376 (2,3,4,5,6,7,8,9) - I think the note density in this part should be decreased a bit so that the flute sound at 00:18:481 (11,12,13) stands out more, also mapping it like you did on 01:39:797 (39,40,41,42,43,44) would be a good choice
01:46:902 (45,46,47) - This could be mapped the same way as 00:18:481 (11,12,13) for consistency
Nice one, overall, just some consistency stuff that hits me. Hitsounding is divine!
Futsuu
00:04:000 (3,4) - you may want to swap these, nothing is going down here
00:06:344 (5,6) - this is even more easiily mapped than Kantan, I think you should swap this pattern with the one you used for Kantan.
00:19:271 (29,30,31,32,33,34,35) - 3/4 notes can be a little too complex for Futsuu especially with plenty of finishes
00:21:837 (37) - this one could be deleted for the sake of difficulty
00:34:863 (55) - ^
01:07:232 (114,115,116,117,118,119,120,121,122) - like 00:19:271 (29,30,31,32,33,34,35)
00:59:732 (101,102,103,104,105,106,107,108) - Increase note density, this is just the same as Kantan
01:22:429 (25,26,27,28) - like 00:19:271 (29,30,31,32,33,34,35)
01:47:692 (90,91,92,93,94,95,96) - ^
This looks like it could be a light Muzu, like seriously, this is some hard stuff! Try to bring the difficulty down a bit so that it spreads nicely.
Muzukashii
00:04:000 (4,5) - like Futsuu
00:12:363 (21,22,23) - I know you're following the strings instruments in the background but you should keep the motif of folowing the flute throughout the entire phrase so make that a 1/2 pattern and make 00:12:758 (24,25) a ddd triplet instead
00:46:113 (121) - just a personal opinion: add a finish?
00:52:824 (144,145) - Ctrl+G
01:49:074 (130,131) - ^ to emphasize high pitched ending
Oni
00:34:271 (101,102,103,104) - I don't think these are necessary
01:50:455 (193,1) - move these back 1/4 beat, they are off
Hitsounds sounded weird, I can't really fix this for you because it would affect the map style and I'm not an expert at those either.
Taikatsu!
00:04:000 (6,7) - like all other diffs
00:06:226 (10,11) - Ctrl+G
00:17:495 (56,57,58) - change to ddk
01:11:771 (340,341,342,343,344,345,346,347,348,349,350) - If youchoose to do 1/6s the whole thing should be 1/6 as I don't see any interruptions of 1/4s. However, I would advise against using 1/6s if you aren't an expert at these rhythms yet.
01:50:455 (570,1) - again, these are off beat
Okay, so for all difficulties, things get increasingly ugly as your diffs goes up. Kantan is a very nice map, one of the nicest Kantan I've seen in my modding carreer. However, as you go up, things get really unbearable. Hitsounding has errors, difficulty spread is having problems, note lacks rhythmic accuracy, etc. I would advise that you review everything. Go through evey difficulty of the set and try to mod your own map. Spot all of the bad parts yourself and then accept more mods. I would say pretty far from ranking.