Black Clover Chapter 339 spoilers showed Asta’s new power-up. This confirms things like Anti-Magic Zone and Anti-Magic Skin and all that Magic and Knights can make based on Mana. These techniques are based upon the unconscious manipulation of Ki that people use to manipulate Mana. This creates Magic. Mana manipulates magic and Ki manipulates Mana. Asta can use any unspecified magic techniques based on Mana and his anti-magic.
As Yuki Tabata demonstrated in Chapter 339 of Black Clover, Asta could use anti-magic spells.
Black Clover Chapter 339: Full Summary and Spoilers

Black Clover Chapter 339 begins second after the conclusion of the previous chapter. Yami’s sister Ichiga grabs Asta by the face, just like Yami does every time. They have the same personality. Asta confirmed that Yami had never mentioned that he had a little brother. It may seem obvious, but it isn’t. Yami never mentioned the existence of a vice-captain or any other Black Bull member. Also, think about how casually Asta said he knew Henry was there all along.
This confirmation is essential because it could be pertinent that Yami has never spoken about his family. Why is that? He might not even be aware that he has a sibling. His family might even exile him. We have many questions when we consider why he never spoke of his family. He called himself and his family fishermen. However, he could also have meant his relatives, the people he lived with. This would signify that he was having problems with his true family. He may have had to become a fisherman as a child outside the Yami clan.
Asta suddenly attracts a lot of attention from the people of the Land of the Rising Sun. This is not because he has a double-arm, at least not primarily, but because they view him as a foreigner. They have never seen anything similar to him in the Land of Rising Sun. They even wondered about his hair color. They understand that Asta isn’t from this country. Clearly, such an event does not occur very often, if ever.
Asta could be the first foreigner to visit the country for years or even generations. This country must have a reason for being so isolated. People in the country are anxious. They whisper behind Asta’s back and pose as if afraid. When people are worried or nervous, we can see their sweaty faces in Anime.
This clearly shows that the Land of the Rising Sun had terrible experiences with foreigners. It could be that they have been at war with foreigners in the past or are so afraid of everyone different that they are scared to make new friends.
Ryu even notices this sentiment in the population. We should certainly keep an eye out for how this aspect develops over time.
The scene changes to reveal that Liebe is healed. This is likely the exact spot where Asta awoke at the start of the Arc. It’s possible that Asta and Liebe got separated, but it could also be a strange coincidence. What is the explanation?
Asta and Liebe could have done the sightseeing thing together, as there’s no plot-relevant reason it was done this way. Tabata may not want to simultaneously introduce too many characters from the Land of the Rising Sun.
Mikuriya Fumito is the name of the new character. Mikuriya Fumito is Japanese, just like the other names in Land of the Rising Sun. Rumors are spreading on Twitter and Subreddits that Tamata created Mikuriya himself and drew him as the new character. Mikuriya may look the same as Tamata.
Fumito revealed in this chapter that it took him longer to get Libre because this was the first time he had medicated such an animal. Fumito refers to such a creature as either a Devil or a creature that does not possess Magic.
Asta can be protected from any Magic by wearing Anti-magic armor. This chapter strongly suggested that there would be an Anti-magic armor that could protect Asta from all kinds of Magic.
The unique no potato meal at the Heart Village is highlighted. Tabata mentioned these potatoes once before, but now he repeats them. This indicates that there is something more to the Land of the Rising Sun than it seems.
Although these potatoes are only found in the Land of Hage, it was revealed that they could be seen in the Land of the Rising Sun. This is a faraway continent from the Four Kingdoms; no one can race there without assistance. Not even Asta, who can fly at incredible speeds using his anti-magic. Only a few options exist. The Land of the Rising Sun doesn’t exist, or it’s an illusion. Asta will either train to be stronger in the afterlife, or this is where he lives. These potatoes are only a reflection of his mind.
Asta asked for his return to the Clover Kingdom again. This time, he panicked a bit as he didn’t believe he could get more vital in such a short time. He was suddenly slapped by Ichika, who told him to shut down and follow her. She wants to show him something, so she takes him to her backyard to see a pile of bamboo sticks. Asta wants Ichika to show him a new technique. Asta becomes confused and says that he doesn’t have Magic. What could they possibly teach him? It is concentration and a sense of Ki that will help him. It’s not just about feeling the Ki but also how it feels.
Asta’s use of his Ki is primitive. This lesson with Ichika is going to change everything. Then it was revealed that Ki is the flow and energy of vital energy, which everyone manipulates unconsciously to control Mana and create Magic.