Quote Originally Posted by Niwashi View Post
It could be as early as level 17 if you're on-level with your Main Scenario Quests (though it is true that many players are over-leveled at that point, so it might end up being after 20 in that case).
And two of them give a total 350 extra item slots (it's 175 each).
Wow, I'm stupid
I even went to count the rows and columns to get the 5x5 per bag, and then missed that I have a second page with 3 more bags and the crystals on my retainers xD
Sorry about that. Yes of course, it's 350 extra slots!

About the quest: I assumed it had to be past 20 since the OP played the game to 20 and had not encountered retainers yet. And I did the quest just this morning myself on my alt, which was 23 at the time without having done any sidequests, so I just assumed that was the natural level you'd be at. I guess SE cranked up the exp gain by a lot to make it easier for new players to catch up