Symbol II: Air and Mortis
So, we all know Mortis' mannerisms are taken from Soyo and her words from Sakiko. This takes me back to the theory that someone said about the ELEMENTS album songs and how it represents each Ave Mujica member.
The Ether MV pretty much confirms it by pairing each symbol with the members: Sakiko = Symbol IV: Earth Nyamu = Symbol I: Fire Umiri = Symbol III: Water Uika = Ether
Finally, Mutsumi, or much more specifically一Mortis = Symbol II: Air.
When the songs and MVs first came out, we didn't have any context since the anime hasn't come out yet, but now, it makes perfect sense.
We don't need to break down much, just reading the lyrics is enough to determine this is Mortis.
"I dance to the sound of somebody's words" (literally how she echoed Sakiko's "fated destiny" talk from CRYCHIC's formation to the eve of Ave Mujica's disbandment)
"I dance in the darkness as I sing, laughing; Hello there, I say with my face stained with tears" "Haha, don't worry, it's nothing" (Mortis has been calling out to Mutsumi for a while now, we know this from Ep2. In the midst of Mutsumi's struggles as she tries to cope with the stress of having her mask off and revealing her identity, as well as the pressure from Sakiko, and the dysfunctional dynamic of her family and Ave Mujica's members, Mortis promises to protect her if she just surrenders. Meanwhile, the plight of Mutsumi is unnoticed by anyone, even those she considered close to her. She couldn't talk for the fear of ruining everything for anyone so, she is forced to hide her true feelings for their sake.)
"But if it’s what the world wishes, then yes," "Be it a harpy or Cerberus, I’ll become anyone" (Mortis is definitely the performer that everyone expects her to be. She is considered a natural genius in this aspect. The want to keep Ave Mujica together meant that Mutsumi had to sleep and let Mortis take over to fulfill the part that she thought Ave Mujica needed.)
"Within the heavy downpour, this soul slowly crumbles to dust, see" (It reminds of the scene wherein Mutsumi saw Sakiko crying in the rain on the day the latter left CRYCHIC. Also, the scene where Sakiko yells at Mutsumi in Ep3. Mutsumi was overcome with guilt which resulted into "her soul crumbling away" or how Mutsumi was put to sleep and Mortis took over.)
"Haha, perhaps this is a just enough reason to govern the flow of time" (In my opinion, this reflects the scene wherein Mortis justified herself to Mutsumi, that the former would protect the latter is she just succumbed. Mortis "governs" the present, including her decisions and actions but she has no memory of Mutsumi, and vice versa, in the event that the host personality resurfaces.)
These are just some of the lyrics from Air that really echoes Mortis and Mutsumi. And to add the cherry on top, Air has the easiest rhythm guitar riff一just a barre chord on the first fret一throughout most of the song. And Mortis doesn't know how to play the guitar, unlike Mutsumi, so it fits the theme perfectly. Furthermore, the piano on Symbol II: Air goes crazy, just like the state of the anime itself right now.
For Fire, Nyamu's entire backstory hasn't been revealed yet but there are bits and pieces of her personality and her narrative that reflects the song's lyrics.
"I'm facing a paradise of weeping roses" "I adventure myself for my heart is determined" (It is implied from Ep4 that Nyamu came from a southern prefecture [judging from the accept/dialect she uses]. She was determined to come to Tokyo and make a name for herself. Tokyo is considered the hub for aspiring artists. Japanese artists who wishes to make it big might have story about coming to Tokyo from their prefecture and having nothing or being alone. LOCK's VA, Nyamu's VA are some examples.)
"No one can speak for perfection" (We all know Nyamu perceives herself as inferior. She is surrounded by geniuses and envies them, without knowing what really goes beneath the surface. She uses clout to her benefit as a means to sustain herself. In order to get that clout, Nyamu has to play a role too, to be her influencer persona to gain fans and elevate herself. For Nyamu, you have to give everything your fans wishes to maintain their support, this is thus, beauty, but then, there is the presence of Uika and Mutsumi who easily charmed people with little effort.)
Now, I'm a bit excited to see how Umiri encompasses Water. So far, we don't know anything about her aside from she plays in 30 other bands and she's classmates with Taki and Uika.