Why didn't I do this sooner...

1. Mokou takes on an aura shaped like a phoenix for her spell cards. Many fanworks portray them as wings of fire instead.

2. Despite killing her on a regular basis, Kaguya seems to regard her as more of a Sitcom Archnemesis than anything.

3. In the final stage of Reisen's story in Urban Legend in Limbo it looks like she's going to fight Reimu for the second time, but she gets teleported somewhere else and Mokou shows up in her place for Reisen to fight.

4. She is somewhat more masculine-looking than most other characters, and one of the very few ones who wear trousers rather than a skirt or dress, so fanon often gives her a gruff and boyish personality to match her appearance.

5. Mokou went crazy for about three centuries by her reckoning, or so she tells Keine in Cage in Lunatic Runagate. She basically spent her time burning anything and anyone she came across.

6. After that she spent another three hundred years in an apathetic depression doing absolutely nothing.

7. Kaguya embarrassed her father (and by extension, her whole family) because the latter presented her with fake items of her impossible requests. Mokou has detested Kaguya ever since.

8. Of all the hands that ZUN hides, hers are the only ones that are actually kept in pockets.

9. Prior to drinking the Hourai Elixir her hair was black, but it eventually turned bluish-white over the centuries. (Well I thought it would be a brownish shade but ok)

Young Mokou and Present-Day Mokou:

She kinda looks like a short-haired Kaguya.

10. During the trip down from Mount Fuji she was overcome by the desire for immortality and killed Iwakasa, the man carrying the Hourai Elixir, and took it for herself. She has regretted that ever since.

11. A funny case - an attentive player can see her dying after each emptied lifebar... and respawn right off the bat. She seems to have some trouble coming back for her last card. Maybe if you killed her enough at a time, the elixir would wear off?

12. Inaba of the Moon & Inaba of the Earth shows that Mokou's cooking is more unhealthy than her starving herself is. She outright says that she thought she was going to die from eating the mushrooms she had grilled for herself... only to immediately correct herself and admit that she actually did die from them.

13. Mokou was planned to be a playable character in Hisoutensoku but got scrapped. While she missed the fighting game after Hisoutensoku, Hopeless Masquerade, she finally makes her playable debut in its successor, Urban Legend in Limbo.

14. In Inaba of the Moon & Inaba of the Earth she is shown to have developed a high tolerance for pain by intentionally taking danmaku point-blank to the face. Wow. Sounds painful.

15. Due to the fact that Mokou wasn't allowed to go out in public, it's believed that she was an unwanted child.