Any idea what "achievements" unlock more friend slots?

Hello,

I was wondering if anyone knew what the achievements were to unlock more friend slots.

At first I had thought I the only way was to play through story and as it goes along you automatically unlock friend slots. However I got one today for beating Alvida's stage 30x as I needed to waste some stamina before leveling with Elite Buggy Stage. (work took longer than expected) Anyone know if there is similar achievements for every single stage or heck one for 50x, 100x on just the boss/miniboss stages?

I think you get one for every story stage and every special stage upon first completion. I don't think there's any other way.

I didn't get anything for Zeff (probably around 40 times), but I heard people unlocking the achievements for Kuro, Arlong, etc, so I'm guessing only the final boss stage for each town.

I asked this question because I got a title achievement when I completed the Alvida Hideout Stage 3, 30 times as it literally said that at the top and I currently have 45 slots, I am guessing now as well that maybe it is the same only for the other boss levels for each map if Zeff stage doesn't give one. (It gave me the Old Hag title)  If someone who did the last Kuro, Krieg, or Arlong stage 30+ times could chime in that would be great.  Confirmation from the actual ones that got the achieve would be nice. That and if there is other ones for more like 50x 100x or whatnot