According to what he had read, the theory talked about Sacrificing the other abilities of the Variant to increase the grade of one ability.
The person who wrote it theorized the way to sacrifice the ability and that it could only work on Variants that had more than two abilities since one sacrifice was needed for the other.
However, it also talked about the chance of failure. There was always a chance that one Sacrifice wasn't enough for the evolution of other abilities. That's why the man wanted to try his theory on a person who had three or more abilities to increase the chance.
At the end of the diary, he talked about how he was going to go on a search to find a perfect candidate who could prove his theory. There was no further entry in the diary there.
Lucifer couldn't help but wonder if the man had ever found his candidate. Since this news didn't spread, there was a chance that he couldn't find the person he was looking for.
