Must be some slang I'm not aware about. Literally just means middle/medium (sized) human. Anyone here know the full context of what she's saying? I speculate she;s calling her a half-pint.

I believe that's exactly what she's saying, theres nothing deeper to the joke than that. Large fairy, Little Devil, and then Middle/Midsized Human.

Wow, Chuningen is very ill tempered!

Average Human.

And then Reimu got a bomb.

Dai-chan's logic is pretty much flawless, though. And as usual she's adorable.

TITLE
ほげ~~~ “Hogeee~”
猫車 “Nekoguruma”

FIRST PANEL
Daiyousei: 私は大妖精 Watashi wa daiyousei “I am Daiyousei” (Big Fairy)
Daiyousei: 紅魔館には小悪魔とかいうのもいるらしい Kurenai ma-kan ni wa Koakuma toka iu no mo irurashī
“There seems to be one ‘Koakuma’ in the Scarlet Devil Mansion”

SECOND PANEL
Daiyousei: では目の前にいるあれは差し詰め中人間 Dewa me no mae ni iru are wa sashi-dzume-chū ningen
“With that being the case, that Medium-Human in front of me after all”
Daiyousei: とでもいうのであろうか To demo iu node arouka “Should be called (Medium-Human) right?” (the order is quite weird here but I normally try to translate as close to the Japanese order as possible)

THIRD PANEL
Daiyousei: とりあえず呼んでみる Toriaezu yonde miru “Let’s call her that for the time being”
Daiyousei: おい中人間 Oi chū ningen “Oi, Medium-Human!”

LAST PANEL
Reimu: ああ！？ “Aa–!?”
ギロッ *giro–* *stare*

Daiyousei: こわい中人間こわい Kowai chū ningen kowai “Scary, Medium-Human, scary!”