Ep 15. The Diamond Mage

Asta and the rest of the Black Bulls receive a mission which takes them to the Diamond Kingdom. They are sent to protect a diamond mage who is a key assets for the kingdom and to stop him from defecting to the Clover Kingdom. The group travels towards the Diamond Kingdom and are greeted by beautiful landscapes, strong and tough soldiers and unrivaled magic that is unique to the Diamond Kingdom.

As the group approaches the castle of the Diamond Kingdom, they are met by the mage themselves named Mars. Mars appears to be a young boy who has a troubled past and has been through a lot of torture and abuse at the hands of his superiors to become the powerful mage he is today. Even though he appears to be hostile towards the Black Bulls, he is impressed by Asta's perseverance, and the two engage in a friendly rivalry. During their conversation, Mars reveals to Asta that he does not enjoy killing people and is often forced to do it by the higher-ups.

As the group reaches the castle, they are welcomed by the king of the Diamond Kingdom himself, who seems to be a kind and wise guy. He gives the Black Bulls a warm welcome and assures them that Mars will remain safe in their kingdom. However, the group's stay is cut short when they get attacked by a group of rogue mages. These mages are trying to defect to the Clover Kingdom and they believe killing Mars will give them the leverage they need to strike a deal with the Clover Kingdom.

The Black Bulls engage in battle with the rouge mages, and it becomes clear that they are no match for the attack. In comes Mars, who uses his diamond magic to create essentially a diamond fortress around the group, protecting them from the rogue mages' attacks. This display of power impresses the group and makes them realize why the Diamond Kingdom is known for its strong and unique magic.

However, things start to go sideways when Mars' superiors are brought in, and they accuse him of being a traitor and defecting to the Clover Kingdom. The Black Bulls have a hard time believing them since Mars himself had confided in them about not wanting to kill anyone and how he was being used as a pawn by his superiors. Nevertheless, the superiors order Mars to step down as heir to the kingdom and choose someone else to take his place.

This situation creates a sense of conflict in the group, and they don't know what to do. They feel powerless, and even though they are there to protect Mars, it seems like there is nothing they can do to help him. Later that night, Asta has a conversation with Mars where he tries to convince him to leave the kingdom and come to the Clover Kingdom. He promises Mars that he will be able to live freely here and that he won't have to kill anyone if he doesn't want to. Mars is moved by Asta's words, and he agrees to leave the kingdom with them.

The group manages to get Mars out of the kingdom safely, but as they leave, they are stopped by a man who works for Mars' superiors. The man tries to take Mars back to the kingdom and threatens the Black Bulls with his magic. However, Mars steps up and shows the man what he is truly made of. He uses his diamond magic to create weapons of immense power and takes the man down easily.

In the end, Mars and the Black Bulls bid farewell to each other, and Mars promises Asta that he will work hard to become a better person. The Black Bulls arrive back at their headquarters, and everyone is in high spirits as they had succeeded in their mission and had managed to rescue Mars as well. Asta is happy to have made a friend in Mars, but he also realizes that there is a dark side to magic as there are those who are willing to use it for their own selfish needs.