While I cannot guarantee I'll be able to fulfil your request depending what it is (especially if it's to find rare items or to visit shops located in Tokyo/Osaka/etc physically because I don't live there!), please do not be afraid to ask! As mentioned on my FAQ page though, I do not take requests for Yahoo! Auctions.
Examples of what I've done previously:
* ordering from websites for goods/special editions of items that only ship within Japan
* ordering from Japanese online shops (goods of other artists I don't usually do pre-orders for, clothes, manga tools, etc)
* buying doujinshi from events
* getting tickets for concerts/stage shows
* buying items from Mercari, Japan's second-hand market app
Just make a comment on this post, and I will reply as soon as I can. Try to be as specific as possible! Being vague will only make the process longer.
I'm also available at kaji.jshop[at]gmail.com if you prefer emails.