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There are two methods I could had approached this process. The first one would have been to transplant the Heart of a very strong Dragon inside of my body, replacing my existing one.
That would have been quite dangerous though, and if it failed, I could had died. Also, we lack the proper heart for that, so it was impossible anyways… I would at least need the Heart of a Dragon at S Rank for the process to be worth it.
And the second process was the one I choose, by consuming multiple Dragon Hearts from other lesser beings and absorbing their power into my own through the Dragon Energy Fluctuation Technique, I forcefully made my Heart mutate into a Dragon Heart.
The process was swift because I've been preparing my body for this moment, constantly cultivating draconic energy thanks to my contract with Ruby, whom I evolved into a True Dragon. Also the other Dragon-related Skills Leveled Up quite a lot lately, enhancing my affinity.