You buy chakra in this feature (rng, something like mysterious cave). After you have some, you c*locate them in corresponding slot (general and 5 elemental). To get ini stat, you need to upgrade all 6 of them to lv 10, 20 etc.

Used 4k, got less than 1k power, lvled up move1 to lv20 on each slot. It gives you 100ini, 1% elemental damage and 1% elemental resist for each 10lvls on move1. Also looks like each slot provides resistances on its own. Fraction of those stats is passed onto move 234. Idk, seems like a high end money dump. Not that useful unless you are literally out of ways to get ini (kinda like purification breakthrough pills, although power gain on paper is nice, but its paper thing)- otherwise you are better off spending on myoboku gift/grasp/training up to map 14 completed.

Propably best wait for someone brawe to do 20k+ spending video on this to see what happens and if its worth it.

Upgrading to lv10 might be worth. You wont notice big difference, but something something minor is there. Level 20 takes too much resources for me. Personally wont touch that system again until im between 250-300k bp, because its simply expensive and provides really situational stats tied to only 1 position, not whole lineup.