Okay then...
Let's start with the eyes. I think that eyes are a beautiful reflection of the person's soul, to which there are many reasons. I would like to note that I will be talking exclusively about the iris of the eye, which to me seems the most capitative part of an eye. I might investigate other parts later.
Let's begin from the physiological perspective.
The iris development is controlled (mostly) by the PAX6 gene, which is vital for many organs during fetal development, including the central nervous system, and the brain. Considering that, it is possible to speculate that iris atrophy/degeneration could be a sign of a neurodegenerative disorder, as has been done in some scientific studies. (I should note that this is solely my personal opinion. Please do not take it to heart if you have such a condition.)
This gene does barely control iris pigmentation however, which is caused by melanin, secretion of which is controlled by HERC2, OCA2 and TYR genes. However, a different factor now comes into play, which is color psychology. It is widely believed (and artificially induced by branding/marketing worldwide) that certain colors can mean certain things, like red for anger and lust, green for peace and wisdom, blue for tranquility, et cetera. This has a close relation to eye color, which could, consciously or not, shape perception of you to others, which in turn shapes your soul due to experiences with those others. Surely you’ve heard of somebody’s eye color mentioned in a conversation at least once in your life.
With this information in mind, let's move onto the spiritual/religious perspective.
In Christianity, which Blue Archive is closely related to, it is said in the Bible that (Matthew 6:22-23) "The eye is the lamp of the body. If your eyes are healthy, your whole body will be full of light.". This is obviously correct, as a not visually impaired person would naturally experience the world of God as a whole. With an outlook on the physiological formation of a human, this also makes sense, as an “unhealthy” eye could pertain to some possibility of a neurological problem.
Now onto the halos. (This relates solely to the Blue Archive universe; a real-life religious introspection will be done at a later post.) The halos are, while at first seen as not unlike the eyes, carry many important differences. While they too are a vital for a Kivotos resident (hereby known as a student)'s development, not having one is lethal to a student, unlike being visually impaired, which is while a very poor situation to be in is still a survivable condition. Furthermore, the intricacy (pattern) of a halo is not seen by a student alike, unlike Sensei, a human, who can see and differentiate between the halos. Thanks to this, we know that a student’s halo color palette is usually the same as their eye color (and also, sometimes, the hair!), with rare exceptions. The “third eye”, the eye of consciousness, mentioned in Buddhism ideology, which Blue Archive is related to as well, allows one to see the world beyond the physical senses and perceive the true nature of reality. It is my belief that Sensei is in possession of such “third eye”, which allows his soul to see the souls of others, as reflected in halos. Why other students do not possess such a “third eye” is not something I am able to explain right now, but I hope to do that with future research.
Fun fact, did you know that Shiroko’s eyes are mismatched, the left being white and the right being dark, being an exception to the beforementioned rule? I wonder if there’s somebody related to Shiroko who prefers dark attire? Pic related.
Fun fact, Arona has the same heterochromia, with her right eye being blue and the left one, which is mostly hidden, being violet. I sure wonder what that means…
Thank you for reading this autistic babble. I hope you riked.
I will continue my analytic research with relation to the use of color symbolism in BA to get a full understanding of its’ use myself and will (hopefully) publish the results later.