How to get that stone you ask? By completing Budokai is how you obtain one of those Dragon Stones. +13 requires 1 Dragon Stone, +14 requires 2 Dragon Stones, +15 requires 3. You cannot go higher than +12 without those stones. Its whats needed for none rng upgrades.
So that would mean every week you can upgrade 7x to +13 +14 +15 (only adult budo) the idea is nice that we get something usefull from budo but because of the lack of players budo is way to easy and 7x upgrade for 1 week is crazy.