Mossari-San

               l^丶            
        fluffy    |  '゛''"'''゛ y-―,     
               ミ ´ ∀ `  ,:'     
             (丶    (丶 ミ     
          ((    ミ        ;':  ハ,_,ハ
              ;:        ミ  ';´∀`';,  
              `:;       ,:'  c  c.ミ  
               U"゛'''~"^'丶)   u''゛"J

            /^l
     ,―-y'"'~"゛´  |   fluffy
     ヽ  ´ ∀ `  ゛':
     ミ  .,/)   、/)
     ゛,   "'   ´''ミ  ハ,_,ハ
  ((  ミ       ;:'  ,:' ´∀`';
      ';      彡  :: っ ,っ
      (/~"゛''´~"U    ι''"゛''u

Two wholesome, fluffy characters. The big one is called Mossari-san (もっさりさん), and the little one is called Chinmari-san (ちんまりさん). They're sort of like Totoro for 2channel.

Of course, like every cute character, they can be victims of abuse.

       |ハ,_,ハ
      |´∀`';/^l
      |u'''^u;'  |
      |∀ `  ミ  ダレモイナイ・・・
      |  ⊂  :,    モサモサ スルナラ イマノウチ
      |     ミ
      |    彡 
      |    ,:'
      |''~''''∪

Origins:

            /^l
     ,―-y -―-'  |   fluffy
     ヽ  ´ ∀` ヽ
     ,| /)     /)
     |        |   ))
  ((  |        l
     ヽ       ノ
      (/ ̄ ̄ ̄U

Mossari-san originated as a round Mona-like character, inspired by Kirby. The fur was a later addition.

The slightly different fluffy and smooth forms of Mossari-san were eventually retconned to be its summer and winter coats.

  winter      /^l
     ,―-y'"'~"゙´  |
     ヽ  ´ ∀ `  ゙':
     ミ  .,/)   、/)  
     ゙,   "'   ´''ミ
  ((  ミ       ;:'
      ';      彡
      (/~"゙''´~"U

  summer     /^l
     ,―-y -―-'  |    ~~~ミ~~     ~
     ヽ  ´ ∀ ` ヽ    ミ~~ ~ ~
     ,| /)     /)     ミ ~       ~
     |        |      ~~ ミ ミ~
  ((  |        l     ~~~ ~
     ヽ       ノ        ~~  ~~
      (/ ̄ ̄ ̄U    ~~ミ ~~~
                  ~ミ~     ~~

Derivatives:

Mossarazu-san

          /^l
   ,―-y'"'~"゙´ヽノ   fluffy
   ヽ_ ヽ ゚ ∀ ゚ノ
      /ノ)  ヽ/)
      `´) ( , }、     .ハ,_,ハ
   ((  / ノ~\ヽ   ,;' ゚∀゚ ; fluffy...?
      ノ/   { |    ~) っ ~っ
     (/     U   ι'⌒u´

Mossarazu-san (もっさらずさん) and Chinmarazu-san (ちんまらずさん) are shaved versions of Mossari-san and Chinmari-san.

Tsathoggua

            l^丶
            |  '゙''"'''゙ y-―, ph'nglui mglw'nafh Cthulhu
            ミ ´ ∀ `  ,:'     
          (丶    (丶 ミ   iä!    iä!
       ((    ミ        ;':  ハ,_,ハ   ハ,_,ハ
           ;:        ミ  ';´∀`'; ';´∀`';,,
           `:;       ,:'  c  c.ミ' c  c.ミ
            U"゙'''~"^'丶)   u''゙"J   u''゙"J

            /^l
     ,―-y'"'~"゙´  |   R'lyeh wgah'nagl fhtagn
     ヽ  ´ ∀ `  ゙':
     ミ  .,/)   、/)    iä!    iä!
     ゙,   "'   ´''ミ   ハ,_,ハ     ハ,_,ハ
  ((  ミ       ;:'  ,:' ´∀`';  ,:' ´∀`';
      ';      彡  :: っ ,っ  :: っ ,っ
      (/~"゙''´~"U    ι''"゙''u    ι''"゙''u

Tsathoggua (ツァトゥグァ) is one of the eldritch deities from the Cthulhu Mythos. It is described by Lovecraft as a furry toadlike creature.

Tsathoggua is served by its spawn. In the mythos, these are formless blobby creatures, but as AA they are just cute critters that like to dance.

The Collared One

         /^l
,-‐-y'"゙"''゙゙"´  |  
ヽ、,;' # ・ ω ・ ミ    I have so much more to teach you...
 ミ====[==]=l==ミ
 ミ   ヽ)   つ;;\ハ,_,ハ,
 ';,        ミ ,;゙#)ω;;,  ...  
  ;;,,      ,;;゙  ミ,;:.~ ̄~,ッ
   ∪"゙'''"゙∪   `'u゛-u'

An AA representation of The Collared One (首輪付き), the faceless protagonist of Armored Core: For Answer. Since we don't know anything about what they look like, this is technically a valid headcanon. The larger character holding their collar is Kasumi Sumika, The Collared One's Operator.

spoilers for Armored Core: For Answer This scene represents Ending 3 of the game, where you destroy Cradle 03 and kill 100 million people.

Sources: