Some questions

1: Fandom

2: Only know users of this ability is Reimu (via Fantasy Heaven or Nature) and Yukari (Her boundary manip allow her Meta-Teleportation who is the ability to teleport anywhere even metaphysical things like out of Reality)
This ability allow you to beimmune to just about anything that would affect or harm them, whether it's any changes or halts made to space, time or reality; any potential changes made will be rectified and restored and regenerated to its original state. Any changes to the reality will be noticed by the user, aware of the differences between the original and any changes. Yukari or Hecatia can't even reach Reimu
so yeah that's broken

3: He create the Mini-Hakerro of Marisa who make Master Spark (who can destroy mountains)

4: The only way for being immune is to have Omnilock (exist above every concepts) only know characters who can beat her are Hecatia and The Dragon God
but it's said Yukari is comparable to gods who are unbounded by any concepts as they predate the existence of any concepts or manipulate and destroy the border of Red/White who represent the beginning of absolutely everything (Red is the blood so life and White is the nothingness) or the boundary of dimension
here for more understand boundary manip powerlisting.fandom.com/wiki/Boundary_Manipulation
so Yukari is broken

5: Oni are Yokai Orges who drink sake and have great strengh
know Oni are
Suika (who shattered the heaven with one punch which are referred to as "paradise", the realm where Amitabha, who is googolplexes larger than the observable universe lives who is egal to be 3.7107x10^152 universes large so a lot of universes)
Yuugi (who is more stronger physically than Suika)
Kasen (a sage of Gensokyo)

6: Ships are fanon, we don't know

7: Only God and Cirno

8: If i not mistaken there are 3 religions

Taoism


Buddhism


Shintoism


9: i don't think Maxwell can Yukari can disable his ability Able/Disable or manipulate the existence of Maxwell Existence/Nonexistence or destroy the border of Red/White who is the beginning of absolutely everything or even Reality/Fantasy so Maxwell get erased from reality and he is just a fantasy, he also can't beat a monotheistic god like the Dragon God, if Maxwell can he would be High nigh_omnipotent, omnipotent
But verse i know who can solo Touhou are (not in order)
in god tier
Umineko (Featherine or the Creator)
Marvel (The One Above All)
DC (Omnipotent being)
Cthulu Mythos (Azathoth)

10: I think that's start with Bad Apple or some Undertale fan say Touhou copies Undertale or something like that
and the war start whit videos Touhou character vs Undertale character
Let's take example

Yukari vs Sans: Some Undertale fans admit Sans lose but others who still say Sans win but don't understand Sans is wall level and Yukari high complex multiverse to maybe outerversal

Sakuya vs Chara: The debate is worst, i see someone say Chara can destroy a infinity of timelines but Chara only destroyed one timeline and Sakuya multiple timelines so Chara is Universal+ and Sakuya Multi-Universal

Asriel vs Marisa: that's here i don't understand, in this fight Asriel stomp Marisa (Asriel Universal+, Marisa Star Level) i thinking 2hu fans will be salty but no, but some other Undertale fans are mad because Marisa didn't die but don't understand it's the pacifist run

Toby Fox is a fan of Touhou and his favorite character was Ran but now it's Yukari (he say it)

i prefer Touhou but i love Undertale but i found the fandom really cancerous, fandom of Touhou can be a little cancerous sometime but i found it more mature than Undertale fandom
i even found this (please don't hit me Undertale fans) hhttps://www.youtube.com/watch?v=0Rp0FuAJguA&t=583s
at least Undertale fandom is not like MLP fandom, FNAF fandom or  even worst Sonic fandom (Sonic fandom ruined my favorite series when i was young)

and by talking about vs fictional characters i need to say something