Huh. Centipede gets a different font now for her private thoughts. Didn't get it during the first chapter.
Edit: To expand...
Hidden because of length
...previously Centipede girl thoughts are written in the same Antique-Gothic font as the other text. This 'composite font' is the main font used in most Japanese manga, named so because it comprises both cursive (Antiqua) kana and sans-serif (Gothic) kanji. Nearly all dialogue in Japanese manga is written using this font style, especially if they are found contained within speech bubbles. Out-of-focus text found outside bubbles will typically use a "maru" variant of the same with rounded strokes around the corners (and less brush 'flourishes), which helps aid legibility for smaller text.
Centipede gurl now uses a Mincho ("Ming Dynasty") font for her private "monster" thoughts. This font has little upwards-pointing "triangles" (called "uroko", "fish scale") near the end of 'brush' strokes, which are basically the Japanese (and the rest of the CJKV sphere) equivalent of Western serifs. So, kinda like a Japanese version of serif font, basically.
The specific Mincho variant used appears to be MS Mincho (or some variation), a common Mincho font that comes bundled with most Windows installations (especially on older computers running on XP or older without many other choices to fall back on). This font is also the usual "fallback" font for most browsers when rendering websites that fail to specify "Japanese" properly under the stylesheet.
MS Mincho is infamous for being... well, UGLY (just look at the thin strokes and that... UGH... 'hook' on い). And a bit illegible. The hatred it causes is not too dissimilar to what some English-speaking speakers would think of, say, Comic Sans MS (Oh look, Microsoft again!). But its usage here is... actually quite apropos because it causes a very 'jarring', somewhat 'alien-like' effect when reading Centipede Girl's thoughts. Quite brilliant of Ishiyumi-sensei too, if it's done deliberately.
TL;DR: Monster gurl uses a monster-looking font. Up yours, Microsoft, for creating this monstrosity, but now it's proven to be quite useful for its unintended role.
Though, trying to figure out what equivalent to use here is somewhat tricky. Anarchy (Danbooru supplies this font under "scary") is too overdone and illegible for text paragraphs. Blackletter also has similar legibility problems. None of the other Danbooru-hosted fonts seem suitable either, except maaaybe IBM's Plex Mono, (hosted under "mono"), but that one sort of has a robotic feel to it instead. Hmm, decisions, decisions. Oh well, going to just use serif for now.