so, i started thinking (which is already a dangerous task for me to do at any given time), and it lead to me asking a question: "Why is WxS Kaito in Solid Heart?" and it sent me down such a deep rabbit hole of realisation that i'm going to word vomit everything into this post.
so first, for the unitiated: during the second april fool's day event, the cast of project sekai was stuffed into a single school: the All Music Mikudemy (or just mikudemy from here forward), and organised into four classes, with one from each unit entering each class. cautious heart, with honami, haruka, kohane, tsukasa, and mafuyu; passion heart, with saki, minori, an, rui, and mizuki; solid heart, with shiho, airi, akito, nene, and ena; and pure heart, with ichika, shizuku, toya, emu, and kanade. but one additional part of it is that the virtual singers also got shuffled into these groups, with one from each sekai (two from vbs) entering the four classes: 25ji miku in pure heart, mmj rin in passion heart, vbs len in passion heart, l/n luka in cautious heart, vbs meiko in cautious heart, and wxs kaito in solid heart.
we know it's these specific versions of the virtual singers because of minor design details shown through their live2d models and the way they behave (or, for miku, it's really obvious she's from the empty sekai). rin having the stage sekai ribbon specificially, len wearing the uniform like he does his street sekai jacket, luka's sweater having the same blue accents and her wearing the same locket, meiko wearing the same earrings she does in the street sekai and using the kamiyama uniform's tie, and kaito having the same mustache pin he wears on his wonderland sekai uniform. there's also the fact these six are considered the "initial" virtual singers of each group and were part of the cast of the 2.5 anni virtual singer event. which was probably what decided who would be part of the mikudemy in the first place.
all of this established, i again ask the question at the core of this: Why is WxS Kaito in Solid Heart? the way he behaves aligns far more with the vibes of cautious heart, especially with the fact he's the initial virtual singer of tsukasa's sekai. his controlled, older brother air (if emu's "kaito onii-san" says anything) matches the way tsukasa feels and behaves regarding saki, that's certainly a large part of what formed kaito into the sekai in the first place. he's the leader of the virtual singer theatre troupe, he handles most of the directing for their shows, he functions as the "straight man" to the comedic natures of the wonderland sekai cast. everything kaito is aligns with cautious heart, not solid heart. so Why?
the short, and probably real answer if we assume colopale didn't put a ton of thought into an april fool's event, is that they otherwise wouldn't have a virtual singer for solid heart. none of the chosen cast fits the description of solid heart, most of them significantly worse than kaito does at first glance, and cautious heart already has two of the major "mentor" virtual singers in l/n luka and vbs meiko. the closest to a solid heart rep beyond what they already have would probably be vbs len, but i definitely agree that he's better fit for passion heart, for reasons i'll get into later as i answer the big question (including but not limited to: keeping len with rin).
but i think there's an actual reason behind kaito's solid heart placement, something i discovered by looking through the other virtual singers and why they fit the classes they've been assigned.
first, let's look at luka, meiko, and cautious heart as a whole, since i already have a short (by my standards) description of what makes cautious heart cautious heart on my blog as is, it's just more focused on why tsukasa's in it in particular rather than about the class as a whole. cautious heart is, by description, a grouping of natural leaders that handle those around them with great care and kindness, often to a point it begins to reflect poorly on their mental health (look at honami and mafuyu). all of them come from some level of "talent"—haruka is regarded as a perfect idol, kohane has a natural gift for singing, mafuyu's... entire story—but where this separates from pure heart, who carry the same trait, is the way this impacts their lives, starting in some way negatively. as their talent brings with it expectation, either from themselves (tsukasa and mafuyu) or the world around them (everyone else), and this expectation is something that weighs heavily on these characters. a massive central part of all of their themes is this expectation, the impacts it left in their lives, and how they move forward with this expectation. some of them leave it behind them (mafuyu), some of them chase with the dream of overcoming it (kohane and tsukasa), and some of them completely redefine what these expectations mean (honami and haruka).
if we look at l/n luka and vbs meiko, we can immediately see a couple throughlines to this theming: namely the factor of talent and leadership. luka is the senpai of the school sekai, having knowledge of all four leo/need instruments to a degree that she can reliably teach the members of the band how to improve throughout their entire story, and being the only one to genuinely test shiho's mastery of the bass earlier in the story. the role luka plays in the stories of leo/need's members matches the role honami plays in the relationships of the band, sharing that same unending drive to care and support the others in the group, something especially shown through her roles in Stella After the Rain and Live with Memories. vbs meiko is very much the same way for the street sekai, being the owner and bartender of crase cafe and holding a mentor role for the other virtual singers and members of vivid bad squad. she doesn't step in to assist with improving their singing until vbs get noticeably better, roughly halfway into their journey to surpass rad weekend, because not only does it provide opportunities for the other virtual singers to provide their input, but her teachings exist on a level above what the others offer at first.
both school sekai luka and street sekai meiko stand on a level beyond the other virtual singers in their sekai, and choose to offer their wisdom akin to a parent or a teacher rather than peer-to-peer like many of the other relationships with the virtual singers tend to be. they are leaders within their sekai, even looked to as such by those that made the sekai they're part of. perfect fits for cautious heart.
then there's rin and len. the former is really easy to assign to passion heart; stage sekai rin takes most after minori, if not clear by her being the least experienced of the six and her role in Hear Me! Hopeful Stage and Connected by Painful Hope (performing two different roles for minori and haruka respectively but they're both parallels to minori's own role in the idol group; rin's empathy and understanding for minori's struggle and the extra perspective she gives to haruka that she otherwise wouldn't have considered). everything about mmj rin connects back to minori in some way, and as a passion heart student herself, it was a given that stage sekai rin would be assigned the same class.
but len approaches passion heart from a completely different direction, something that adds a new perspective to the class and their stories. because on the surface, len would be better fit for solid heart: his relationship with akito is one of the core dynamics of the street sekai, he's constantly in competition with street sekai rin, and even to some degree with miku (mirroring the early dynamics between akito and an), and he played a major role in akito's chapter of BREAK DOWN THE WALL. most of the evidence points toward solid heart vbs len, but i believe the part that puts him in passion heart is the fact rin is a given to go there. because rin and len are a pair. they share a number, they're both kagamines, and across every sekai they have a special relationship that works as a motivator for at least one member of the sekai. and out of every group, it's vivid bad squad that puts the most emphasis on the importance of partnership. it's a massively central and unendingly important aspect of its story and the growth of its characters.
street sekai len takes this pairing of rin and len to an extra level, as their relationship is the example of vivid bad squad's partner dynamic. every time conflict arises between the two, it's ultimately born from wanting to be a better partner for the other; something that's directly paralleled across both the bad dogs and the vivids. entire plot points are built from the importance of this dynamic, the fact they are the most important people in each other's lives (not even in a shipping sense, this is just direct storytelling; to deny that fact is to deny the essence of the group itself), and that manifests itself into the dynamic of rin and len. a pair of virtual singers whose relationship transcends sekai. no matter the circumstance, no matter the personality they're given, they are partners.
and when you look at passion heart through this perspective, you can immediately see a pattern: every member of passion heart strives to embody a certain light they were given. saki with tsukasa, minori with haruka, an with nagi, rui with tom gray, mizuki with yuuki. and, within their own groups, their stories develop their characters through their relationships with others, having entire events around a particular, vitally important person: saki's Parallel Harmonies with ichika, minori's entire dynamic with haruka, an's entire arc from Bout for Beside You to Whip the Wimp Girl!!, rui's relationship with tsukasa after the main story, and mizuki's My Footprints, Your Destination and Our Escape For Survival for ena and mafuyu respectively.
passion heart is built around its relationships, the importance other people play in their lives and growth. to not include the inseparable pair of rin and len in that class would simply be a mistake.
this brings us back around to kaito and solid heart. what about wonderland sekai kaito connects him to the themes of solid heart? well, if school luka and street meiko are cautious heart students at the ends of their journeys, and street len is a new perspective on the meaning of passion heart, i think wonderland kaito is meant to be both of these things. because kaito is the solid heart connection to cautious heart, a representation of what they're capable of by embodying a class solid heart often envies.
wonderland kaito pulls a lot from tsukasa's character (obviously so, as a manifestation of his emotions), and tsukasa's story, despite himself being cautious heart, reflects the themes of solid heart. specifically the events On the Stage of Dazzling Light and Towards the Phoenix at the Sky's Edge. stories about tsukasa's struggle to perform as the actor he wants to be, the latter specifically putting him in a position of intense longing for a goal he feels is lifetimes away from him. yes, both of these are for the sake of the character he's playing, but that reflects perfectly in the stories of solid heart, who put their all into their work to achieve the goals they've set out for themselves, and will put themselves through the most difficult climbs just to reach the top of the cliffside. if the way his story presents itself wasn't better fit for cautious heart, and nene wasn't already a perfect solid heart student, tsukasa would be solid heart. and kaito, carrying such a major piece of tsukasa: his dedication to his craft, is the solid heart within tsukasa. the drive to grow, the will to keep pushing no matter the challenge, the willingness to try anything that might lead to success, even if they get hurt in the process. yes, he acts more like cautious heart, but that's the point.
shiho has always been an odd one when it comes to solid heart's themes. yes, they act like a member of solid heart (all the way down to the common mischaracterisation of them being an asshole, a universal trait of solid heart characters), but their story has always worked in contrast to the rest of solid heart. solid heart characters come from a position of inferiority, feeling the need to overcompensate and push themselves to their limits in order to "keep up" with the rest of their groups' capabilities. shiho has never had this struggle; they've always been skilled, the most experienced member of the band. shiho has an entire event, Don't Lose Faith!, that has ichika confront them about the fact they hold back to not outshine the other band members, so they don't glow too bright and take the glory for themselves. it's the opposite of what solid heart has always needed to do. because shiho, like kaito represents, is already there. their drive was uninhibited by their environment, save for the struggle to find a band they can participate in. their actual ability as a musician has never been hampered by the world, while the rest of solid heart run off the belief they're worse than their group because that's what the world has told them, directly or indirectly. shiho is the sunlight that solid heart is capable of achieving.
so wonderland kaito, much like shiho represents, is an embodiment of what solid heart can do with their determination to grow despite the challenges. because they look up to the cautious heart students, they're envious of their skills and talents. but kaito is the proof that they can be that.
that, i think, is why kaito is solid heart. the virtual singers are representations of these characters' feelings and aspirations, and wonderland kaito serves as an embodiment of the goals of solid heart. their mission to be like the cautious heart students that seem to have everything together. kaito shows them that it's possible by being like cautious heart but still solid heart.
