"Lower One’s Eyes" is a level 26 expert chart, which is a purely comparative system of difficulty measurement. It’s often considered the hardest level 26 chart in the game due to its swing rhythm and frequent usage of “flick notes”, which require rapid but precise finger movements.

"Bug" is another level 26 chart many consider to be uncharacteristically difficult. It is a very high BPM song that features repetitve quick note patterns, along with particularly difficult intro and outro sections. To add insult to injury, if you like to watch the music videos for each song in the background of the rhythm game (like I do), you have to deal with visuals that require an epliepsy warning.

"Kitty" is a level 28 expert song, which is the threshold between normal charts and what are colloquially called "boss songs". I don't find the bulk of this chart particularly difficult compared to similarly leveled songs, though the outro can easily trip me up. "Kitty" is the most difficult expert song from Nightcord at 25:00, a fictional music group from the game whose songs are my favorite.