Convert Blu-ray animes to 720p 100mb average how?

you can probably do it in VLC, I've used VLC to compress video several times now for work use. take 1.6 GB HD video and compact it down to website friendly size as small as possible and without losing too much quality.

I dunno exactly what i do, I just try a few different settings and compare quality vs size,

i generally use ac3 sound, h 264 and output mp4.

you probably won't see 100 mb file sizes though, my 720p anime files are average 350 mb. although that's probably because i'd rather have quality than small file size. there are 100 mb or less versions available, but i know you make noticeable sacrifices in quality when you do that, as well as reduced image size.

In order to enable Blu-rays on Plex, try H.264 MP4 as output video type. If you would like to preserve original DTS-HD Master audio track, chapter markers, and subtitles, I know ByteCopy can help with that because of its marvelous ability of multi-track MP4 output.