spoil?

You want spoilers, so I'm gonna spoil, others should be wary in that case:

Asta ist plain human in and on itself. He doesn't have an ounce of Mana in his body, which is strange enough, but he got chosen by an old Grimoire, which was lying around for hundreds of years. In said Grimoire, a woman, who was actually Asta's mother, sealed a devil who also didn't have an ounce of Mana. He developed the power of Anti-Magic while fuming with rage for years, until the Grimoire moved into the hands of its new owner and thus, the devil got in touch with him too. He can utilize the powers of the devil, as the book is now his and the devil, called Liebe, is bound to it. But Asta himself ist no more than a devil user (and not even that per se, at least not in the beginning), he himself is a normal human.

There's one part I'm always confuse about is that the Grimoire used to be Licht's but then there was no devil inside the book and Liebe was sealed in there alone?? No Licht's devil there?

The one thing that is unclear about all of this to me, to say that first, is how Grimoires really work. One time, the Grimoire intact right beside FuFu-goleon means he's not dead (yet), but they need to hurry, since it's starting to dissolve (as in, it's a sign for his impending death). Another time, for some reason, people steal Grimoires (or attempt to) to sell them to collectors and Licht's Grimoire was left behind, too, so they didn't dissolve after death. I'm sure there might be some kind of rule behind it, but they didn't make it clear yet, which kind of irks me a lot. Aside from that little fact, to answer your questions:
The Grimoire used to be Licht's. Licita, Asta's late mother, found the book somehow in the secluded woods she called her home, just a few days prior to finding Liebe, a little demon without magic power, in those exact woods. She raises him for a while, in place of the son she had given up on (Asta), but when they are both attacked by the devil Lucifero, who channelled himself through Liebe somehow, she get's fatally injured and didn't want Liebe to be exposed to danger all alone. So she took the book she found earlier, which had the five leaved clover on it, used her power to seal things or beings in smaller containers to put him into the book and dies. Then the Grimoire chose a new owner for himself - Asta. So when Licht had the book, it turned because of the forbidden magic he used, but there was no devil in it, that happened waaaay later.

thankssss

Woah I see... Thank you for your explanation tho... But now I'm curious, how did Licita get her hands on the five leaf clover Grimoire when Nero sealed it together with the First Magic Emperor at Asta's and Yuno's village there? And now I understand Licht's forbidden magic, is that Licht is the devil himself not the Grimoire I was kinda confused there for a sec...
And your question to the Grimoire didn't dissolve when Licht died... Maybe, In My Theory that is when someone died of an old age, the Grimoire is picked up and to be chosen by the next generation, but when someone is not fated to be dead yet or didn't die of old age, the Grimoire is dissolved?? Idk but that's what I think of the Grimoire... But thank you tho for your explanation ヾ(❀╹◡╹)ﾉ~

The Grimoire that Secre sealed away was that of the first magic emperor, not Licht's, as far as I remember. At least, I never really questioned it, because that's what I picked up.
Well, Licht got killed and it didn't dissolve. The same goes for Fana. Though, she didn't die, that might also be true, but she got a new Grimoire after being taken over by the Elf Fana. But when FuFu was close to dying, it started to dissolve right away, so that's kind of weird.

Oh wait what?? Oh my I think I have to rewatch it I'm very confused lolo but thank you for the explanation