I consider myself a long ways away from bilingual- but I know enough to get my message across. (At which point my friends go 'ahhh' and correct my grammar- for which I am grateful. Japanese is a hard language- I wish you luck.)
I know several people who are on the forum have experience living in Japan but none of the people I looked out seem to have their comics available in Japanese, which is too bad.
One of the comics I'm subscribed to, Faerie Gari, the creator mentions in its description it was originally in Japanese- but there is only English available, sadly.
The only webcomic I can think of is Yuumei's series Knite which has gotten a number of translations, including Japanese (on the first chapter only, sadly.) however Knite on tapastic itself does not have any translations available- but in case you're interested, here it is all the same. (The deviantart versions are flash comics and cannot be read on mobile to my knowledge.)
KNITE (first two chapters only) on Tapastic: here
KNITE CHPT 1 日本語 on Deviantart: here
KNITE CHPT 1 English on Deviantart: here
If you look on the deviatart account for the Japanese chapter you can find numerous other translations available as well, for anyone else.