First, your future self went to the timeline that is bound to be erased in the near future.
After that, he met Neal and made a deal with him. In the end, he blessed him with the death energy and respective platinum-grade Arcana (bone sword), which consumed his original Arcana, fire salamander. As a result, his DNA has been modified.
Then, he placed Neal 14 years prior to the timeline of his counterpart of this timeline (Neal). During that process, he used the tenth soul skill: the Rewrite to change Neal's identity forever.
Now, you should understand that this method is quite risky.
If something goes wrong while you are rewriting the timeline of an individual who doesn't even belong here, then, the entire timeline will be at the risk of going unstable.
The unstable timeline, depending on its range, might destroy everything into nothingness and you will incur the wrath of the gods.