Warning! Spoilers ahead for Black Clover chapter 322!
Yami Sukehiro just swooped in to save Nacht Faust - and by extension Asta - from certain death, reviving a trope in Black Clover that would have annoyed fans if not for how it actually saved the series from an even more egregious sin.
Yami isn't the only character in Black Clover who has the tendency of arriving in the nick of time. Asta and Yuno subject each other to the same level of one-upmanship. But in Yami's case, the first most memorable time he participated in this now stagnant trope occurred during Asta, Gauche, and Theresa's first battle against members of the Eye of the Midnight Sun. Asta and his friends wouldn't have had a chance against the Eye's leader if Yami hadn't arrived. But in Black Clover's 322nd chapter by mangaka Yūki Tabata, Yami's ability to protect Asta and Nacht from the King of Devils Lucifero's devastating blow actually prevents Asta from becoming even more over-powered than he already is.
Until now, Black Clover had set up Asta to undergo the stereotypical awakening of the shonen hero. Asta had attempted to defeat Lucifero but was soundly beaten to the point where other high-ranking Magic Knights had to protect him. Ironically, Yuno's contributions to the fight could have been Black Clover's way of fulfilling another popular formula, where either Yuno or Asta saves the other and then they take down the opponent together. But Tabata brushed that trope aside by making Yuno's magic ineffective against the devil. Instead, Asta rose - battered, bruised, and not in his devil union form with Liebe - to help Yuno, even though he could barely keep himself from falling back down. Better yet, Nacht later arrives to help Asta and loses. All of these elements - plus Nacht's death at the hands of Lucifero - would have been the perfect ingredients for an awakening. When shonen heroes are up against a wall and have no hope of winning, their unfortunate predicament unlocks some latent power inside of them that allows them to overwhelm the enemy. Yami actually has a variety of expressions to describe this phenomenon, such as pushing past or going beyond your limits - or some variation of the two that describes surpassing or exceeding one's limits.
Yami's ceremonious entrance is the preferred alternative to Asta bringing Yami's catchphrase into reality as it keeps the boy from getting too powerful. Asta has already achieved a milestone in his journey to becoming the Wizard King by forming a union with Liebe. This allows him to utilize the full extent of his "black" form and leverage what has already been identified as their world's savior from the devils' invasion: anti-magic. By the accounts of Black Clover's harsher critics, Asta is already too powerful, especially for a kid who has no magic whatsoever. So, the fact that he still needs to be rescued and can't always just "push past his limits" to save the day makes him seem even more of a realistic hero than he did when his fellow captains had to sacrifice themselves to protect his unconscious body.
Of course, Asta still has limitations. He can't hold his devil union with Liebe for long, and when that time runs out, he has to wait 30 minutes before forming another union. But shonen usually find ways for their heroes to break down these limits as though they're nothing. The fact that Asta wasn't in his devil union form at this time only increased the chances that he would have somehow unlocked a new power to defeat Lucifero. But luckily, Black Clover prevented that from happening. Now readers just have to wait and see how successful Yami is against the so-called King of Devils.