Great job for creating a simple, fun meta-dating game that builds up a charming atmosphere through whimsy writing andgeneral intrigue. It's nice to know that a game could be fun purely based on the creator's charm. (Note: The 5th ending is impossible to reach due to the game defaulting to ending 2).
Although, with so many looming questions, it was impossible for me to not theorize (I am completely overthinking this silly little game). Here is your obligatory spoiler warning.
Let's start with the rules of this universe. Within the game, I have managed to identify 3 separate entities: Kira, the narrator, and the player. Kira and the narrator are often at odds with each other. i.e., the narrator might have information that Kira doesn't know or speak independently from her. Kira also directly refers to the player separately from the "victim," who is revealed to be depicted as nothing more than a severed mannequin head (both revealed in ending three).
Throughout the game, these three entities drive the story forward. The narrator communicates with the player, while the player communicates with Kira. The narrator and Kira do not appear to be aware of each other. Both, however, I believe to be victims of the laws of the universe.
Using context clues, we can piece together how the universe operates. Despite being labeled as a good ending, ending 1 concludes with Kira ominously telling the player to continue the game. This is backed up in ending 4, when Kira describes the truth: she only exists when the game runs. Her existence, then, is similar to the meme in which its caption explains that a character will stop existing when the viewer scrolls, followed by a terrified aforementioned character.
Kira, interestingly, doesn't seem to realize that she is in a game, as she never mentions the player as such or eludes to programs, data, or otherwise. Even though she does distort similarly, akin to a glitch, Kira never specifically takes note of her actions as anything out of the ordinary. The narrator shares similar limited knowledge. Events such as "obtaining an ending" never cause the character to realize that they are in a simulation. Instead, it is almost as if they believe that they are in a time loop. Alternatively, this game may not actually be self-aware. This can safely be ruled out, however, as the game actively uses glitches as motifs for its atmosphere.
Following the idea that the game is self-aware but none of its characters realize this, oddities start to appear when the game operates outside of what it should. For example, when you tell Kira that you don't know who she is, she responds that her mind feels fuzzy. Also within the 5th ending, the narrator states that the game world keeps looping upon itself endlessly, despite it being implied that Kira would have needed to walk down a flight of stairs to receive your food.
P.S. There really isn't a good place to put this, so here will do. Ending 4 has Kira go on a rant about how she's expected to be a love interest in this world on a blank slate, like some dating game character. She adamantly states that she is as real as you and doesn't deserve to be stuck in the predicament she's in. What's more interesting is that before she says all of that, she alludes to other conventional romance game elements, such as having the player be loved by all and only hated by the "villains" or "rivals." No other characters appear in the game besides the narrator and Kira, leading me to believe that the world's structure is based on a conventional dating game but fails to have all the content that comes with it.
Despite Kira being the poster child for the game, I believe that the narrator is more important to the story (that either doesn't exist or is not intended). Most of the time, narrators are nothing to note about. If they are important, they are either revealed to be the internal monolog of the player character or a separate character entirely. This game follows the route of the second option but introduces the idea that the narrator may be tricking the player by fabricating the truth. Ending three reveals that the entire date had been a "practice." No one was actually bound to the chair, and instead Kira was speaking to a mannequin head. This revelation would imply that Kira had made up the entire game in her head, but that is false, as ending 5 depicts a conclusion without Kira entirely. If this is true, then why does the narrator continue to make comments that would only make sense if you were actually a person bound in place?
The mannequin has no arms to reach out for a knife—arms that can't be freed by gnawing. Because of this, I believe that the narrator is making the player believe in a situation that does not exist. If the narrator is willing to distort the truth to keep up the false image that the game provides, what else is the narrator doing behind the scenes? Ending 5 depicts the narrator revealing to the player that the world endlessly loops, explaining Kira's absence. This action implies that either the narrator can move through the world somehow or that the narrator already knew that this was possible. It is not implausible that the narrator knows more about this universe and that they may have an ulterior motive, such as doing anything in their power to keep Kira confined within the playworld.
With everything that I have noted, I will attempt to summarize the hidden lore about this game. I admit that I'm probably just overthinking this. Also, I like to think of it as a testament to the creator's ability to make a silly dating game.
Kira's world is designed to be a dating game for the player. The narrator helps aid this agenda by creating a situation alongside Kira that resembles a date. The world is quite crude, however, hurting the characters whenever the player doesn't play the game. Along with that, it also cuts corners, removing anything that is believed to not be necessary, like the outside world, and instead breaks down when its limits are surpassed. Kira doesn't believe that she's in a game, despite occasionally glitching out and doing things that don't make sense.
Poor girl. Being stuck in dating purgatory is a nightmare.