Known from the description, the 1st kiai is made by YuEast, 2nd and 4th are made by Hatsuki. I feel the three parts a little different. Maybe there are some problems.
In the 1st kiai, the long notes grace: 01:06:009 (66009|3,66009|2,66085|1,66161|0) - 01:06:918 (66918|3,66918|2,66994|1,67070|0) - (sample) toward the same direction, and they all lined up as triple grace, while in the same part of the 2nd and 4th kiai toward the opposite direction, and they all lined up as quad grace. Maybe to adjust the lineup should be a good idea.
Since this is a collab map, it's okay to have a small difference in kiai sections to intentionally show difficulty progression to the map structure itself, as for the first kiai section, I'll leave it to YuEast to answer. Thank you for that suggestion though :D
it's okay to have difference in different kiai part though it's a bit unusual. e.g. https://osu.ppy.sh/beatmapsets/1721052#mania/3521250
also OD 8 seems a bit high for this kind of map? idk
00:28:737 (28737|0,28812|2,28888|1) - rice notes depicting flute, but has been voiced earlier as 1/4 LNs
00:30:214 (30214|2,30271|3,30328|1) - LN sound representation is slightly off
00:15:782 (15782|2,15896|2) - shield representation is off compared to the rest of the song
01:01:237 (61237|0,61237|3,61293|1,61350|2,61407|3) - rice transition in mid-LN build-up feels weird
01:57:600-01:58:529 missing LN for vocal?
02:28:737 (148737|0,148812|2,148888|1,148964|0) - now the notes are LN notes in this section instead of rice? intentional or not
02:30:214 (150214|2,150328|3) - wrong LN placement
02:47:600-02:54:873 - large audio contrast to the rest of the song (low instrumental) but note density doesn't reflect that
02:47:828 (167828|0,167941|1) - sound is not on the correct snap
02:05:100 (125100|3,125176|2,125252|1,125328|0,126009|0,126085|1,126161|2,126237|3) - inconsistent LN ending snaps feels very awkward
02:57:600 (177600|0,177828|3,177903|1) - consider normalizing endings
refering to 00:28:055 (28055|0,28282|1,28509|2) - these notes, where its the same instrument (sorry its not a flute its like a piano or something)
oh i got what you mean. i use 1/6 rice because there's not so much space and will be too hard if using LN there
for 01:01:237 (61237|0,61237|3,61293|1,61350|2,61407|3), it's more of a personal choice, it does fit in my opinion which I played it numerous times during test sessions whike 02:47:600-02:54:873, nerfed the first part of the break section, rearranged notes for 01:57:600, while for 01:58:529, I'd stay with the current pattern since I dont really see any problem with layering in that section
02:30:214 (150214|2,150328|3) - made this rice instead
02:47:828 (167828|0,167941|1) - fixed the snapping problem
02:05:100 (125100|3,125176|2,125252|1,125328|0,126009|0,126085|1,126161|2,126237|3) - stretched the first and second column to the blue line