Return of the voidblade

in a world where monsters and demons exist, every human has a class placed upon them by ancient beings who called themselves warlords, the warlords are treated like gods, to be able to protect themselves from the demons and monsters. Everyone receive the class when they turn 15 years old. there was 6 warlords: the sword warlord, the magic warlord, the bow warlord, the berserker warlord, the potion warlord, and the strongest the voidblade warlord (also known as the katana warlord). There was a legend that said that the 6 warlords almost defeated the demons, but then the voidblade warlord betrayed the others and become the demon lord, the other 5 then tried to kill the voidblade warlord, but in the end they only manged to seal him in the cost of there own lives. And now he is treated as the evil warlord. there was once a boy named Yami from the shinkuu house a noble family that is known for their excellent swordsmanship the head of the house (yami’s father Mitsuo) even has the sword saint class. Yami who was very good with the sword, was still hated by his father, because his dead mother was from a political marriage, and his father never wanted to marry her. Yami was a very kind boy even to commoners, and he was Finally at the age of 15 and could get a class. At the class receiving ceremony his half twin younger brother Hikari was up first, because he was favoured by their father ,because his mother was the woman his father actually loved, got the sword saint class, everyone cheered for him and even his father was happy. However when Yami was up he got the class: lowest tier swordsman (false). Everyone was shocked even Yami himself, and no one even know what the (false) meant, not even the priest himself. At that moment his father said with a cold look on his face “from today you are no longer my son nor a part of this family!!”. Yami begin to mumble to himself “even though i trained every single day with the sword pushing myself beyond my limits until i collapse and was almost at the level of sword mastery, so why, (suddenly yami begin to scream) why is this happening to me?!?!?”. People begin to whisper to each other “did he go crazy?”. Mitsuo called to the guards and told them “throw him into the abyss dungeon, for ruining our family honour!!”. Everyone suddenly begin to cheer “yeah throw him into the dungeon, that’s what he deserve!!”. The guards held Yami who didn’t even resist. Yami suddenly said in a low voice “even though i have been kind to everyone, you didn’t even appreciated it, maybe i should just stop?”. Suddenly Hikari said “that’s what you get for being born to a mother who's so hated by father, big bro, it’s just like i always told you, just go die like the piece of trash you are!!”. Suddenly Yami come back to his senses and shouted “mark my words i will come beck for revenge, you will see even with the weakest class i’m going to become the strongest!!!”. Everyone started to laugh at Yami’s words as the guards took him to the carriage that headed to the dungeon.