we have seen licht can use the same sword as Asta and we have seen so far that Asta is the only one with the 5-star grimoire. Asta and Yuno both are orphans where Yuno seems to me like a son of royal because he is having a very huge amount of magic power like royalty. I think the pendulum in his neck will reveal his identity in the future. We already know the Licht was about to become the dad when the elf was attacked and everyone is dead. but what if Licht able to safe his son life? before his wife dead like he did with other elves soul. I think Asta is the son of Licht.
it seems like Asta is Half ELF and HALF human... that is why we only able to see half part of him become demon.