On the planet that you find Lymle "Lamaria" or something like that, the castle like area that you need to collect shining stones to turn over pillars to access the top levels. There are three sets of battles on the bottom-most floor that you can easily set up to be ambushes, Once you fill your bonus bar with SP chips you get 14 SP per battle, with 8 battles being on the bottom floor you can gain 112 SP per run if you battle just the monsters on the bottom floor. At first it may not be really easy to defeat them, but once around level 25 or so you should be able to defeat each enemy in one combo, and defeat the entire floor of enemies in about 5 mins. This equates to some serious SP, I left "Lemuria"? with over 2000 SP and I've kept everyone at or Above level 5 on all skills (except field skills which I maxed at Lemuria) since then without any problem whatsoever, and I've still got over 1000 SP at all times. Super simple grind with amazing results.