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And above all, my Spirit Stat rose by 20. This means that with every Spirit, it might increase by +10? 10 Stats might seem little, but every 1 stat, they get +5 to all stats, so +20 already gave them +100 to all stats in return, pretty amazing. And if that wasn't enough, the Familiars summoned from cards get +2 from every 1 Spirit Stat, which means that at 70 Spirit, they get 140 to all stats, also quite a useful little buff, which once stacked with things such as Command, might make even the low-grade Familiars quite powerful.
My plan for Ruby is also similar, I'm going to buff him through the roof and then make him kill D Rank and above Monsters, so he can level up quickly. I've heard that dungeons produce monsters by the hundreds, they're perfect to grind to my heart's content. One of my primary drives to join this academy to begin with was the easy access to a variety of dungeons the students use to go level up.
Check "The Protagnist's Sister Is Actually the Strongest"!