I have a solution i came up with for us free to play players,
but it takes patience and taking advantage of happy weekend.
so you can start from today
do your daily missions and the like, but dont spend over 10 energy
wait for it to refil.
When you are done, you can start grinding materials
whenever your bar fills up, use skip tickets (or manually if you need the tickets, recommend giving friendship equips since it will build up over time and you need to get like a kajilion characters to friendship 5 for the cc.)
so you do ten runs of the material of your choice
you will almost always get atleast 1-2 of 2 energy things. But you also get increased drops of the materials, which is a god send for materials for zenkai units.
that way you are building up 4 valuable materials although it takes a while
(energy, souls, saving skip tickets, friendship points)
I recomend focusing on one soul at a time, start from the 7* ones because they will also give you materials for the previous one, which will save you time in the long run.
when you manage to reach the point where you have maxed out capacity it will go to your gift box
which means you can take full advantage of the recycle shop for more valuable materials like erasers, and zenkai materials.
i am currently maxed out on dual coin tickets, which allows me to buy anything i want and just claim the gifts waiting to refill them.
if they are close to expiring i buy extra z power for units like revival cell that need it.
its a similar case with souls
soon enough you will have everything maxed out