Knights of Pen and Paper +1 Deluxier Edition

All you need is 5 characters at one time, in a single play through, to be at least level 30. They also do not need to be at the table (in your squad) at the same time. I had two characters over level 30 sitting idle at the pub, two at the table above level 30, one at the table that had just got 30, and two at the table under 30 when I got this achievement.

As mentioned by HeartsForBuddha this achievement might have some bugs associated with it. Get this achievement either with your first play through or last but do not try to have multiple playthroughs going on at the same time.