Rina

Rina is one of the 4 girls that Arashi entrusted Ryouta to look after. Rina is revealed to actually be an angel like Kuro, but she is known to not just be an angel, but a special breed of angel that was born with a dark half inside of her. Even so, Rina is always quiet like your typical angel and carries around a pet cat since she is obsessed with cats.

Appearance
Rina looks a lot like a character named Primula off another anime show called SHUFFLE!. Rina looks like an 8-year old who really has been around even longer than Arashi, Dartz, and Ryouta combined. She has light purple hair in bows and wears dark clothes. When she shows her angel powers, her left wing is white while her right wing is dark to show both of her personalities inside of her.

Relations with Others
Rina shows a lot of relations with the other characters.

Ryouta: Rina shows affections for Ryouta which could be love relations or strong relations as like a brother figure to her. Even so, she tends to help out Ryouta a lot in times of need.

Kuro: Being also an angel, her and Kuro have developed a relationship showing their bonds together as angels.

Natalya: Since Rina is an angel, Natalya doesn't really like her but Natalya will be willing to rescue her if Scott or Ryouta gives her the order to.

Altera
Altera is the other half of Rina. Altera is released when she is captured by the siren and starts working for Jahrvis in the X Realm. When Altera was dueling, she used a Death Demon deck where the monster would have ungodly points as well as effects by being Normal Summoned or Special Summoned by way of their respective Demonic Spell Card of the same letter. There was also one Trap card in the deck which Special Summoned her 5 strongest and deadliest monsters, though this card was never needed.

Vampire Queen Crystella
While in the Demise Realm, Rina's body is used as a host for the Vampire Queen Crystella who was hired to take out Ryouta. She used a Vampire theme deck which focused on Special Summons and Synchro Summoning for the Vampire Lord Synchro Monsters. Her monster get a nice 1000 point bonus thanks to the field card "Dracula's Castle" which can simply be obtained by discarding a Spell or Trap card to the graveyard.