GeneralI think the difficulty gap between Muzu and Oni is a bit big, in terms of SR and the gaps between the other diffs.
Kantan00:25:649 (13) - This note could be moved to 00:25:464 to follow (insert the instrument here lol) better. Alternatively, in this section here (from 00:24:168) since you're primarily following the bass beat 00:25:094 (12) could be moved to either of the white ticks beside it to coincide with the bass beat.
00:30:094 (19) - I think k would be better here to match the pitch. d for low, k for high appears to be the general idea? It doesn't seem like the notes are mapped to the bass beat here.
00:32:316 (23,24) - Going off pitch, ctrl+g these notes?
00:36:020 (29) - Change to k?
00:38:242 (33) - Change to d?
00:38:983 (34,35,36) - Try k d d or k d k?
Futsuu00:34:538 (74) - Is this enough of a 'drumrolly' kinda sound to warrant a slider?
00:36:390 (76) - Everywhere else in this section a d was mapped to this note. Consider changing this to d to match?
01:21:575 (181,182,183) - Considering 01:09:723 (153,154,155) is kdd and these are essentially the same notes (but an octave lower), it'd be good for consistency if these two 3-note patters were the same.
Muzukashii00:14:908 - A note could go here (probably d?)
00:47:871 (170) - There's nothing that resembles a drumroll at all happening in here, doesn't seem like a slider fits. Maybe use a spinner to fill the gap?
Thought this diff was nice.
OniThe first section is a huge spike in difficulty from the Muzu, though it fits well imo. Unless you're planning on adding another difficulty in between, maybe consider turning some of the triplets into single notes. 00:01:760 (10,11), 00:03:242 (21,22), 00:04:723 (32,33) could be removed. 00:05:557 (39) could be taken out too.
If you're shortening the stream at 00:39:723 (240), maybe remove 00:40:186 (245)?
00:42:316 - A note could go with the beat here.
00:47:871 (289) - Same as the Muzu, I feel a slider doesn't fit here.
01:04:908 - I'm not exactly advocating for more difficulty, but seeing as you already have streams in the difficulty you could put one here, since for the most part these other sections are relatively underwhelming for the Oni. This would probably mean you need another diff to even out the spread.
Hope it helps