I forgot to mention that yami does have a sacred gear that links him to the dark souls word and does a few other things

Name - Vul  Deadheart

Title - dragon god of dark magic

Race - dragon

Gender - female

Power - dark magic

Age - older then great red and ophis

Size - 3 time bigger then great red

Looks

Sacred gear form

Just a sowrd called Gevul gral (dragon tunge for darken destruction)

It's infused with dark magic and destruction magic making it one of the strongest blades in existence able to be on pair with Excalibur fully together.

Blaze can also teach yami a few spells that are as followed but yami has not learned them yet

- Dark Lighting bolt
Creates a lighting bolt made of both lighting and dark magic and girls it at an opponent 

- Dark fire ball
Creates a fire ball that is made out of both fire and dark magic, that can increase in size and hurls it at an opponent

- Dark Lighting storm
Creates a dark lighting storm that effects a wide area of opponents

- Dark magic lance
A lance made of pure dark magic and hurls it at an opponent that attacks both physical and spritaul forms

- Dark magic greatsword
A dark magic greatsword that attacks a person's life force and magic supply

- Dark magic shield 
Creates a shield that can increase in size to block both physical and magical attacks

Human form

Human name - Vul sovut (Dark drag.)

Age - 19

Height - 5,3

Likes - cake, yami, zoom, magic, dogs, katanas, kimonos, fighting, using magic, learning new things, and cooking

Dislikes - perverts, rias, issei, akeno, people who act above everyone, 'privileged' people, Sophie (sister), and devil's