Disclaimer: I do not own Black Clover, or any of its associated characters and lore. That right belongs to Yūki Tabata.
Asta couldn't believe his eyes when saw his home of Hage Village ransacked while he was out training with his new grimoire. Thankfully, no one was tortured or killed, but pretty much everyone was robbed of food and money, and those who tried to fight the attackers off, like Asta's closest friend and rival, Yuno, were badly hurt. The whole event awakened within Asta a thirst for revenge he never felt before, which was when Mariella came in.
A Diamond Kingdom assassin, Mariella and her unit had been tasked by their superiors to hunt down deserters from her own country who were probably causing a war between the Clover and Diamond Kingdoms with their actions. It didn't take much for Asta to figure out that it was those same deserters that plundered his home.
When Asta decided to ask Mariella why she was telling him what she knew, she answered. "Normally, I'd be against letting non-Diamond Kingdom citizens involved in one of our covert missions, but you're different. I saw the way you defeated that former Magic Knight by negating his Magic, and after informing my Commander, Galleo, he's as eager to see your handywork as I am."
Asta saw the logic in her words, but couldn't help but feel that he was a step away from betraying his own nation. "It all sounds tempting, but how long would I work for you?"
Placing her right hand on Asta's shoulder, Mariella showed him a small yet kind enough smile as she replied. "Don't worry. As soon as the traitors are dealt with, you will have our blessing to go home."
Returning the small smile with one of his own, Asta forced a nod of agreement even as he blushed from the close contact. "All right, I'm in."
Giving him a quick kiss on the cheek, Mariella blushingly responded. "Pack what you need and meet me at the Demon's Skull tonight. We'll be waiting for you there."
"Was it really necessary to get the village involved, Sir?" Mariella asked Galleo later at night where Asta was supposed to come. She was still not happy that her unit attired themselves as bandits and laid the attack on Hage Village themselves to acquire Asta's power for the Diamond Kingdom's own use.
Galleo merely rolled his eyes before replying. "Whether these Clover heathens deserved it or not is immaterial. All that matters is that we strike down the traitors where they stand. If people from other kingdoms have to suffer, it is for the greater good of our own people. Besides, our highest authority is rather interested in the Anti-Magic brat, so while you may have given him your blessing to return to his quiet life, he'll remain involved no matter what."
Mariella grimaced, but conceded that she had no choice in the matter. Asta's fate had already been decided just like her old teacher, Fanzell Kruger's, was. The greater good of the Diamond Kingdom as Galleo and the Mage Scholar, Morris, described was what mattered at the end.
Had this thought on SpaceBattles way back. Felt like a good idea to pair Asta up with a female character from a different place other than the Clover Kingdom such as Mariella of the Diamond Kingdom, so here we are. I'm pretty eager to see who else from the Diamond, Heart, and Spade Kingdoms we'll see in time. Even if I don't have a full-length idea for a Black Clover story yet, I still enjoy writing about it.