As a Keito-is-Midori’s-AKATSUKI-senpai truther, thank you for giving me an excuse to talk about them.

Mizuhanome-sensei
When I first started getting into Enstars lore I was like “who the hell is Mizuhanome, where can I find more?”

“He would read me books, or tell me made up stories. I was always thrilled to hear them… He often drew me pictures, too. They are all my treasures.” (Eichi, Quarrel Festival)

Before attending Yumenosaki, Keito wanted to become a mangaka. Mizuhanome-sensei is the pen name Keito uses for his doujinshi. It’s Keito worst-kept secret, but he still attempts to keep it discreet for the sake of Akatsuki’s image (Philosopher's Guidance)

In !-era, Keito draws posters for events around campus and keeps up his manga as a hobby. He has an eye for graphic design and data visualization (Philosopher’s Guidance). He’s more familiar with traditional art than digital. (Philosopher’s Guidance, Scroll of the Elements). Anzu is his biggest fan, constantly letting his secret slip out to others. Her art style resembles Keito’s (Tea Party).

One known work of his is "Wonderland Alice VS. Looking Glass Alice" ("“A fairy tale of love and excitement…" - Eichi). It's unfinished, so Eichi entrusts Anzu to finish drawing the rest (Tea Party). Mizuhanome has written text-only fanfiction for a discontinued series (Biblio) and has a fanart book (Mission of the Spy).

Stories with mentions of Mizuhanome include:
Quarrel Festival (!), Tea Party (!), Comic World (!), Philosopher’s Guidance (!), Biblio (!), Scroll of the Elements (!), Mission of the Spy (!!), Yuzuru FS1 (!!), To Want Even the Help of the Emperor (Eichi) (!!). Souma also mentions him in Colorful Autumn (!).

Midori and Manga
Midori’s taste in manga is a little broader than his love for mascots (Manga Club, A Detour Encounter). He and Mao read American comics in A Normal Day (!).

Midori and Artists
Midori's behavior towards different artists in ES lies along a spectrum depending on how skillful the artist is and how close he is with them.

1) He quietly admires Keito’s art but is distant because of their unfamiliarity with each other (Scroll of the Elements)
2) He’s affectionate towards cute art styles (Shinobu, Souma, Kanata) (Shinobu FS2, Ninja Clan, Colorful Autumn)
3) He’s really affectionate and intense when it comes to cutesy surrealism– aka people who aren’t so good at drawing (Yuzuru, Tetora) (Yuzuru FS1, Colorful Autumn).

Anzu fluctuates between 2 and 3, depending on whether she draws normally or caters to Midori’s interests. Please read Colorful Autumn. I beg of you, it's hilarious.

Midori and Keito
In Scroll of Elements (!), Keito and Midori are the first to arrive at their gig. To ease the atmosphere, Keito uses Midori’s mascot merch as a reference for the pamphlets he’s drawing. When Keito takes the lead on their studies for the Manga Quiz in Manga Club (!!), he settles Midori’s nerves with encouragement and flatters his strengths afterward.

If it interests you, the stage play adaptation of Pirate Festival (Extra Stage ~Destruction × Road) retcons the lore of Captain Kidoairaku (the mascot Midori becomes infatuated with) so that Keito is its creator.