5. "RE: DSMP-PF03: Fait Accompli"
In response to message #1
Fujiwara-no-Mokou and Kaguya Houraisan (nee Fujiwara in this one) are characters from Touhou 8- Imperishable Night. To summarize a long and complicated backstory:
Mokou (and Kaguya in canon, but not yet demonstrated here) gained ressurective immortality from the Hourai Elixir. This power comes with the standard Touhou insane-lack-of-limitations. Also in canon, Mokou and Kaguya are "mortal" enemies, though Mokou has some severe tsundere issues regarding Kaguya, and the latter is aware of this and makes use of it.