Well actually, I don't know if it's any good.

But I was with my Japanese friend today at Book Off and apparently
this series is very much recommended. The series is published a few months
every year.

It is a collection of short stories from new authors and is published periodically.
Maybe 4 to 6 stories per issue and the books are about 300 pages.

It's written for 十代, which is ages 10-19, so it's mostly aimed
at teenagers (my friend is mid 20s btw).

This is the book that was purchased:
http://www.kadokawa.co.jp/bunko/bk_detai...0712000219

Here are samples pages from another book:
http://www.kadokawa.co.jp/tachiyomi/bunk...0902000464

For someone that has finished RTK, the difficulty level doesn't seem too bad.

Anyway, my friend seemed really excited about this book.
So maybe it's worth a try.

This sounds pretty cool, I've been meaning to find some short story collections. I think I might pick this up next time I go to Kinokuniya