Rekka no Honoo, Katekyo Hitman Reborn! Recommendations
main character both use flames, and they have gardians
Like Rekka no Honoo there is flames but its not just that its also because both main characters learn they will be leaders of special groups. The main characters also have to protect a girl with special powers. They have friends who fight with them and both have swordsmen who use water for their swords. They also have to fight for the title to be the leader with another person. The only difference is that Rekka was already a talented fighter while the mc in this is a weak no good boy and doesn't want to be the leader.