detail in diary of undercover observation that i like
a lot of people have noticed how the My R girl isnt wearing shoes due to the custom of taking off your shoes before jumping off a tall building in japan, but i havent seen nearly as many people mention that the girl in diary of undercover observation isnt wearing them either.
it's implied that both of of them are seen in the PV for the song, seemingly on the same "ground" (kind of, they're both on a yellow background with no floor, but you get it), which implies theyre on the same "height" level, that she was also standing on the ledge without her shoes on.
from what ive seen, one of the most talked-about details in My R is how its implied she was about to jump off due to taking her shoes off and standing very close to a ledge on the rooftop of a building. but some of the art made for diary of undercover observation features a certain, potentially tall building..
..which is likely connected to the same rooftop that was in My R. while there may not be a fence here, it's implied that the girl who was referred to multiple times in diary of undercover observation is the person in My R. considering the 2 of the main shots of them are someone with pigtails and someone with a cardigan (that's referred to as yellow in both songs!), which lines up with who/what the My R protagonist talked about, it's likely she's the same person. and thus, the same building/ledge/whatever.
her shoes can't be seen, but standing that close to a ledge without them on could be implying that she was planning to do the exact same thing the protagonist in My R was.
considering how the whole song is about how she feels like her entire life is about observing other people instead of being an actual person, which is (in my eyes) further reinforced by the fact her song is mostly her talking about every other song in the album and other people's experiences instead of her own, feeling like she has nothing noteworthy to write down about her in the small section where she talks about her own feelings, i think it's easy to connect the dots between those feelings and what she might've been planning to do.
the last lines of the song in its english subtitles are
"I'll say something to her today."
"Something I don't even really think."
which is a direct reference to My R!!! it's the same thing the My R girl did!! and in some versions, there's "ねえ、やめなよ" (Nee, yame, na yo) at the end, which is what the My R girl said to the people she had met on the rooftop as well (which are theorized/implied to just be herself).
she tried to stop the My R girl from jumping off, despite her own desire to do so. the same way the My R girl tried to convince herself not to jump.
anyways i just thought that was a very cool little thing