Specifically from an actual animated show, or any heavily autotuned J-pop? Autotune is pretty much ubiquitous in both: are you looking for examples of heavy autotune in anime, or performances that are intentionally highly autotuned to sound robotic as a style?
For the former, Symphogear has a very big library of songs that are sung by the characters in-show, and a very big collection of character albums with different artists. I'd reckon Hibiki's (Aoi Yuuki) songs are usually the most heavily processed.
https://www.youtube.com/playlist?list=PLAczZ-JQo06flJlxngq9vbWzTvFN7O3FFFor the latter, I can name a few examples used in OPs/EDs/general J-Pop, but not a full playlist of songs with intentional over-the-top pitch shifting and autotune. Especially ones where the character herself sings it.
You might want to look into Denpa as a genre if you aren't already familiar, which is all about over-the-top nonsense moe vocals and fast earworms. Very stereotypical "otaku media" music, leans a lot into the "anime girl singing a song" feel, and a fair bit of shows used to use it in 00s. It's quite easy to find playlists for it, but might not be exactly what you're looking for.
https://www.youtube.com/watch?v=VFlvngWRYFkhttps://www.youtube.com/watch?v=4LxxogwcXnU 
