You can level up intelligence actions (called Bravery) by having 'em trigger often during missions. Bit of EXP each time until level-up and then grants bonusses.
honestly, I oughtta redesign this interface soon. I fear if I add more actions it's going to get hard to get an overview of them all.. maybe let the menu be 2 or 3 rows? What about some kind of search/filter...?