Q: Given that you seem to love MBTI (Myers-Briggs Type Indicator), can you give a rough estimate of each character's type?
A: Got so long, I moved it to it's own blog post.
Utako: INFP (Fi-Ne-Si-Te)
I originally typed her as ENFP, but I think she's Fi-dom and Ne-aux as opposed to Ne-dom/Fi-aux. The INFP is usually said to be the most extroverted of the introverts, and I feel like this fits Utako well, since she isn't really an extrovert or an introvert.
As for functions, Utako is so Fi. Everything she does is based off of her values, and she tends to disregard what's expected of her in favor of doing her own thing. Her Ne is what makes her so easygoing and open-minded. Her tertiary Si comes out sometimes, such as when she's remembering her father or using her instrument skills to learn new ones. Her Te goes largely unused, but she can be very blunt and rigid when she's mad.
Aya: ESFJ (Fe-Si-Ne-Ti)
Aya isn't Fe in the traditional sense of keeping harmony and loving others. Aya's Fe manifests in her constantly needing Takahiro's validation and trying to be the perfect daughter in the queen's eyes. She wants to uphold what she thinks will gain her the approval of others, and this is mainly what causes her to clash with Utako's more Fi-centric "I do what I want" behavior.
Apart from her Fe, her Si plays a huge role in how she acts. She speaks in more antiquated terms than her sisters and can be stubborn in her ways. She tends to stick to what she has always known and expects others to do the same. Her Ne isn't used especially often, but it is the root of her moments where she's more easygoing and willing to see things another way. Her Ti goes even more unused.
Shizuka: INFJ (Ni-Fe-Ti-Se)
Shizuka is the type of person that tends to stick to one interpretation of something instead of considering an alternate point of view. This is largely a Ni trait, and it's what the core of her route's conflict stems from. She's so set in thinking that everyone is criticizing her and only changes her mind when that thought is disproven right in front of her (inferior Se).
Her Fe plays a huge role in this conflict as well: she values what other people think of her, which is why she isolates herself so they can't hurt her feelings. Shizuka is a sensitive type, and the smallest thing can make her feel attacked. Her tertiary Ti is what helps her put her stories together and figure out a problem, and her inferior Se really only comes into play when one of her Ni thoughts is proven wrong right in front of her.
Hinata: ISFJ (Si-Fe-Ti-Ne)
Hinata isn't the type that enjoys change, and tends to stick to routine and predictability. The only problem is that for the majority of her route, she is in the grip of her inferior Ne, so her dominant Si gets overpowered by it. Despite this, her Si is still clearly dominant, as Hinata tends to stick to what she knows and has an eye for detail, noticing every little flaw in something instead of just seeing it for what it is.
Hinata uses Fe in that she is very open and expressive with how she feels (probably the most out of her sisters), and doesn't just bottle up her feelings like the Fi-using Utako and Mai. This makes it a bit easier for Takahiro to deal with her problems, since she tends to just tell him how she feels. Her Ti makes her strive for accuracy and precision, which is apparent in her perfectionism. She's in the grip of her inferior Ne throughout most of her route, which is what makes her worry about everything that could go wrong, even if it's ridiculous.
Mai: ESFP (Se-Fi-Te-Ni)
Mai is extremely Se. She's attuned to her surroundings, just living in the moment and taking it all in instead of looking for deeper meaning. This is further exemplified by her being the most athletic of her sisters, as well as having a talent that involves a lot of focus and physical ability. She's also the sister that's most likely to act on impulse, such as pushing Takahiro in a lake or kissing him in front of a crowd.
Mai has Fi as well, in that she desires to have some sort of way to stand out among her siblings. She internalizes her feelings and won't talk about them until she can't take it anymore. When she finally remembers what makes her unique, she embraces it while still trying to learn something new for fun. Mai's Te doesn't get much use; she isn't exactly the most logical person. Her Ni is largely unused as well, though when it does come up, she can be very insightful.
The Queen: ESTJ.