Aptitude trouble?

Simply reincarnate the character and you'll be able to go on more Chara World runs.

Its a semi-slow process. At most if your looking for Aptitude spheres and Heart Conservatives, you'll get around 15 Aptitude up's total. The fastest way is really just burning through the levels and killing off the boss and redoing and not worry about the floor destruction (save for the special null blocks). Also make sure your character is at least level 80 as you get the max bonus aptitude points from the boss at this level (more then if you just did it at level 1.

Once you do it 3 times (assuming your reincarnating as genius) then just reincarnate again at genius. (I level them up first to help contribute to the stored levels first). Then rinse and repeat. But it is a slow process.

Unique characters gets 5% to all aptitudes each time they reincarnate, up to 5 times, which equals 25% to each aptitude in total.
That is quite a lot already.
Other than that, you just have to run the chara world over and over.
I'd recommend getting into the lands of carnage before starting to grind aptitudes.