I don't know how common Koichi is... Haven't noticed lots of them. Don't think I've met anyone named
Noa in Jpn. Never heard of someone named Mayo... Could be short for Mayoko, I guess, but I don't know why anyone would call a kid just Mayo 'cause it sounds too close to the condiment. I meet occasional Chihiros, but not sure how common it is... It's not uncommon, but it's not one I encounter oodles of...
Izumi is pretty standard, but I don't think it's overdone. Have met 2 gals named Mahiro in the past couple years... Both are in elementary school right now, but a few yrs. apart. 1 has an older sister named Yuwa, which is rare.
Love Michiko... It's what I want as a mn on a daughter and I actually met a gal w/ the exact kanji I would use when I was up in Iwate volunteering recently.
I live in Japan again now too. If you're finished uni, you may find the JET programme interesting... application season starts soon for people to arrive next
July.
Just remembered another name that's common on little girls this past decade...
Yuri... Seems like another standard.
Oh... and ka has been a common ending on girls' names the past few decades as well.
Kenji makes a person think old man, but it's a standard and you very occasionally meet a young one.
-ko names people still use:
TomokoKeikoHirokoYoko NorikoEriko
Sakurako (think that one's kinda recent)
maybe Kayoko
Reiko or Rieko (maybe)
All of those are much less common on young children than they used to be though even if they are still usable.