Reasons

"Indeed," the mule confirmed.

"No one has ever created concentrated essence. And no one knows its use… or is it really the case?" 

"As an apology, I'll tell you about it… not that it'll benefit you." The mule paused for a moment. "The concentrated essence is different from the normal essence. The concentrated essence is actually proof that fusion is possible.

"In the past fifty years, no one has ever managed to combine essence because they're reacting to each other.

"However, this concentrated essence is the proof that something like that is possible. There are only two usages that have been found so far. The first is poison. 

"During a super injection, your body is absorbing the essence of numerous beasts. However, all those essences are not combined. They're flowing at their own pace, as a result, your body can handle one or two essences at once, allowing your body to adapt.