The story of Sayu's creation from Humble Beginnings as revealed by her boss fight collectibles is actually pretty sweet. Tila, her voice actress, merely began as a fan of the character when Sayu was just an OC on the game's Bland-Name Product version of DeviantArt. She used an image of Sayu in one of her music videos without permission, and when it started to blow up in popularity, she contacted Sayu's creator, Remi, to apologize. Rather than getting mad, Remi loves her song and decides that the two of them should collaborate. At some point, Sofa and Dodo got involved as well, and thus four internet friends created one of the biggest stars of Vinyl City.
After Sayu's defeat, her creative team seem to be at Mayday's mercy. But instead of beating them up, Mayday simply compliments that they are a talented team. Her only complaint is that they never animate Sayu's Reverse Mermaid form ever again, but that's just about it. She warns them not to get involved with NSR so they won't get further caught in the cross hairs of the conflict.
Though it quickly goes downhill as the fight goes on, when Yinu's mother enters the fight by saving her daughter from the first fall, the prodigy is genuinely happy and grateful, gleefully sneering as her mother quietly encourages her to ignore B2J's bullying and show them how magnificent she truly is. The mother even attacks in synch with Yinu's tempo at first, showing just how well the two can work together. Even after her mid-battle Sanity Slippage, her first response to being saved from the Showstopper is praise.
After Yinu has been defeated, Yinu's mother is about to go on a rampage on Maday and Zuke. ...Until she hears soft, sweet piano music. After calming down, the mother realizes it's her daughter playing on her damaged piano. Though Yinu is as sad as the music she plays, it's enough to reach out to her mother and make her realize she had pushed her daughter too hard, and how much she previously lost sight of why she plays piano. The Mom begins to play on the other broken half of the piano. Soon, the two are playing together, signifying that they are mending their bond as mother and daughter, having remembered why they love to play music.
Their family photos tell a story that Yinu's late father taught her to play piano from a young age. After he passed away from a disease, Yinu and her mother kept his photo on their piano to remember him. This paints a poignant but lovely picture that the two play piano to keep the memory of Yinu's father alive. Worth noting: Yinu's mother still wears her wedding ring.
The epilogue reveals that Yinu's relationship with her mother is on the mend, as the two have continued playing piano side-by-side.
Upon her defeat, Zuke approaches Eve as she truly is: a vulnerable, broken, insecure girl named Nadia. He takes the time to apologize for abruptly leaving her and tells her she has self-worth and that she completes herself. She is finally given not only closure, but peace of mind. This is pretty kind, given the videos imply she's always suffered from self-loathing, and a lonely sense that no one can relate with her.
Unlike the previous bosses, the ending of Eve's fight has her album cover change twice. The first new one shows Eve's symmetrical face in the background, tearing up as her world is shattered. The second cover? The way she and Zuke face away from each other may represent the bitter end of their relationship, but the background shows her tearful eyes closing with relief as her complexion becomes an asymmetrical swirl of pink and white. It's as though it represents her finally coming to terms that she doesn't need to be perfect to love herself.
Mayday acting as a third party during the third and final rap with DK West, mending the brothers' bond. The cherry on top is when the two decide to establish a truce with a handshake... before they hug it out instead.
Another small moment during the final rap: Normally when a verse ends, the player has to smack West's shadow monster to deplete his health bar, and if the bar is emptied before the chorus ends, the two will Kick Them While They Are Down. The exception is the final verse of this rap where the two immediately stop their attack after landing the final blow.
The brothers drop their animosity so quickly once Mayday tells West the truth. Zuke's been angry at his big brother for the better part of a year, and West's resentment is implied to be far older, but once West is open to listening Zuke has nothing but good things to say. West, in turn, seems to abandon all his prior accusations once he's got reason to believe he misunderstood his little brother's actions in college, and is the one to initiate the hug. Only made sweeter by the string of easy health items for Zuke to scoop up in the final stretch.
If one buys into the theory that Yinu's piano once belonged to her late father, then it makes it all the more sweet when the piano is repaired, prompting Yinu to thank Bunk Bed Junction in an overjoyed voice.
Mayday having newfound respect for Tatiana/Kul Fyra, especially after they work together to stop Kliff from destroying Vinyl City with NSR's own satellite. Towards the end, not only has the experience helped Tatania warm up to Bunk Bed Junction, she also makes peace with her past and lifts the ban on Rock music. Better still, she makes it known that from this day forward, NSR will be more open-minded and welcome all styles of music. As a peace offering, she gives Mayday (whose guitar was damaged during the climax) her own guitar from her days as Kul Fyra.
The context behind why Tatiana gave her guitar to Mayday: she recognizes that although her love of rock&roll has returned, her days as a performer are behind her. In that regards, she sees Mayday as a worthy successor of her old guitar and her legacy.
As a final friendly salute from the other artists, Tatiana says "long live rock" while they hold up the rock sign behind her, DJSubatomicSupernova included. Even Yinu, who looks flat-out adorable doing it. (The only ones who don't hold up the rock symbol, however, are Sayu, who strikes her own cute pose, and Eve, who just rolls her eyes.)
Tatiana's final monologue in the epilogue. Special mention to how she uses DJ Subatomic Supernova, Yinu and her mother, and Eve/Nadia as the following examples for why people play music:
Tatiana: It's a funny world we live in. You often get caught up in your own beliefs that sometimes, you need to take a step back and see that the stage doesn't just belong to you. We're all in this together. And the sooner we acknowledge that, the quicker we can work towards a common goal. Everyone plays music for different reasons. Some do it for self-importance, some do it to bond with their loved ones, and some do it to understand their purpose in life. The important thing to know is this: there are no wrongs answers. If we give everyone the opportunity to play their own music, we can build a world where creativity has no boundaries. Well, I'm happy to say that Vinyl City is steadily heading towards that direction. Never have I seen our lights shine so brightly, and it is all thanks to not just NSR alone, but to the performers, the fans, and everyone who resides in this magnificent city.
The final scene is of Zuke and Mayday about to meet their cheering audience, along with Kul Fyra's guitar. As opposed to the previous scene where Mayday was deeply saddened by Bunk Bed Junction's previous actions, it seems our two rock&rollers have gotten back their spark.
