She is the only appeared character in Touhou Project who has a political career.
The final stage title "Yawaragi (Wa) wo motte tattoshi (toutoshi) to nasu" (和を以て貴しと為す) which translates to "Harmony is to be Valued" (Iku also used this quote) gives a clue to the identity of the waiting boss. This is a quote from article I of Seventeen-article constitution which was made by her (= Prince Shoutoku). The quote is continued to say "Sakarau koto naki wo mune to seyo" (忤ふることなきを宗とせよ) meaning "Honour the Avoidance of Defiance" which is quoted in her spell card No.101 and No.102. Making this constitution was her biggest achievement in her political career.
Her Abilities "listen to ten people speaking at the same time" comes from a famous legend of Prince Shotoku. It's said that Prince Shotoku was so smart that he could understand ten people questioning him all at once and than able to give them back perfect answers.
Because Prince Shotoku's ears are so sensitive, this is the reason Miko wears earmuffs.
The butterfly that Miko uses in some attacks probably relates to the story of Zhuangzi's butterfly dream, a very well-known Taoist philosophy stories.
Miko (神子) could mean "Child of God", "Shrine Maiden" or "Sorceress". Her last name, Toyosatomimi (豊聡耳) means "Abundant Clever Ears" referring to her ability. Prince Shoutoku was sometimes called 'Toyotomimi' (豊聡耳), the same kanji as 'Toyosatomimi' when read in today's style.
Assuming Miko is Prince Shoutoku, Miko was born in the 7th Februrary, 574, making her the only character whose full birth date is known. Remilia and Flandre's birth years are known, but not their month and date.
It is said that Prince Shoutoku was married to "Iratsume no Toziko" (刀自古郎女) who is thought to be Soga no Tojiko in the Touhou world, and "Mononobe no Futsuhime" (物部布都姫) as Mononobe no Futo would be her mother-in-law (Remember that this is not an official fact).
The accessory which Miko wears on her ears that look like headphones are actually earmuffs. ZUN have mentioned in the Nikennme kara hajimaru radio that she wears them to prevent her from overlistening to too much desires.
You can see the kanji "Wa" (和) is written on her earmuffs. What's written on the other side is unknown because the angles of her picture are limited. But it is likely that (貴) is on the other side because of her famous line "Harmony is to be Valued" (和を以て貴しと為す).
The straight sword which she hangs by her waist is assumed to be the Shichiseitou (七星剣), a Taoist sword of Japan's national treasure which Prince Shoutoku had believed to have.
The stick-like thing that she has in her hands is called the shaku (笏). Prince Shoutoku has it in his pictures too, it is used as a cheating paper in events like ceremonies which is a bit funny because for him being an all-time genius he wouldn't have needed a such thing.
The colors used in her dress comes from the Twelve level cap and rank system, another major achievement that she made.Greater Virtue represents 1st rank and Lesser Virtue for 2nd rank.
In Ten Desires, when you enter spirit world mode/trance mode, the music changes. Miko's theme doesn't change though. This could be because she can listen to spirit's desires so this could be why it doesn't change in spirit world mode.
Her Energy Bar icon in Hopeless Masquerade is a reference to a meme known as Reaction Guys or Gaijin 4 koma.
Miko's left hand in her Ten Desires profile happens to be drawn incorrectly. Her fingers should be showing while her thumb should be hidden. However, if you consider that the left hand's finger which the viewer sees is a pinky, everything looks normal.