Good Is Not Nice: She does what she can, and occasionally feels regret for those she can't help, but in the end her job is to banish Shinma, not to protect or save people. She's not above using mortals as bait, if necessary.
Guile Hero: The girl is frighteningly manipulative and good at playing people, specially in the OAV and in spin offs like Vampire Yui and Vampire Princess. Very, very few people are able to outsmart her.
Empty Shell - The Stoic: Miyu's dad, since Miyu's mom drank his blood before marrying him, which she regrets due to the terrible effects. It's actually so bad that when the Shinma came to claim Miyu as the Guardian and both his wife and daughter ran away, he simply stood there quietly, allowing the Shinma to capture him.
Mama Bear: Miyu's mother tried to save her from becoming the Guardian by force. By either trying to kill her (manga) or giving her her own blood (OAV). It didn't work, obviously.
Parents in Distress: They're now hostages of the Japanese Shinma, frozen in time and in an eternal sleep in an alternate dimension between the Darkness and Earth. Miyu has to catch all the runaways to get them free.
Good Is Not Nice: Reiha fights the runaway Shinmas and all, but she's not concerned with the bystanders at all (whereas Miyu sometimes gets Pet the Dog moments towards them and values the few human friends she does have) and openly antagonises Miyu.
Cute Mute: When she "wakes up", she doesn't say a single word.
Deal with the Devil: She let Ra-en possess her body and use her for his plans, in exchange for creating an illusion in which her parents are still alive.
Despair Event Horizon: Her parents's deaths. Since they died after giving her their blood so she'd survive, poor Aiko blamed herself and called herself a vampire, biting the neck of her doll in the orphanage she was placed in much to the horror of the other kids. Then Ra-En came in...
Dead All Along: They actually died in a car crash a while before the OAV's take place.
Good Parents. Or so they seem. They were this when alive, see the trope below to know more.
Heroic Sacrifice: They knew that their injuries from the accident would eventually kill them, so they begged their treating doctor to let them donate their own blood (of a pretty rare type) to Aiko so she'd survive. He couldn't refuse such a request since they had no blood of said type left in the hospital and there was no time to ask for donors: in the end Aiko survived, but Mom and Dad died.
Stepford Smiler: He hides his boredom with life in general, his feelings of inferiority towards his more academically-succesful siblings and his apathy towards his Education Mama's constant pressure under a polite, soft-spoken, beautiful mask.
Kill the Cutie and Stuffed into the Fridge: Chisato kills her and Yukari as soon as her powers awaken. In Hisae's case, Chisato does it under the effects of the Shinma Shidon's More Than Mind Control right after she and Yukari learn the truth about Miyu, then wakes up next to the dead Hisae and starts screaming in horror...
Fat Girl: She was noticeably chubbier than the other girls
Empty Shell - Fate Worse Than Death: Since Miyu cannot undo the damage that has already been done to poor Miho, she ends up biting her and taking her blood. The last time we see the poor girl she's hospitalised, listless, completely indifferent to anything around her...
Magic Feather: Cruel subversion: the red shoes she was given as lucky charms... were actually a MacGuffin that absorbed her life energy.
Hot Scientist: In charge of the local aquarium and some experiments. Not really.
Graceful Loser: Escaped years ago from Miyu, so when she finds him again, he at first tries to cover for his girls and help them escape, but once he loses he doesn't put up much of a fight and lets Miyu vanish him.
Bad Dreams: Sorta. Yui first saw Miyu in a dream, in which she started telling her about their bonds. Then Yui is woken up by her Old Retainer and starts her usual day... and then Miyu appears in her school...
Break the Cutie: Specially when she can't control her urge for blood and ends up draining one of her school friends, then runs away in horror and when she arrives near Yuki's "Pool of Illusions" and Nagi tells her who she truly is without any filter.
Cherry Blossoms: Weaponised by Yui, who can manipulate and bend them to her will. It comes from Yuki, whose powers sorta can manifest through Yui.
Shouji reveals to Kyouko that Yui had always been fascinated by the massive cherry tree in her garden. She actually hates it, as she thinks that whenever sakura trees bloom, someone she loves will die.
By the end of the first volume, all that's left of Yui's old home are the sakura trees.
Half-Human Hybrids: One of the oddest examples ever in this franchise. Mother is human, father is a Shi (another kind of demon, described as "the anti-Shinma"), and she also is half-vampire as her mom was given Miyu's Kiss of the Vampire when still pregnant with Yui. That's not counting her connection with Yuki, the former Guardian of the Lake and leader of her vlan, whose succesor and twin sister Saki was Yui's ancestor.
Foil: To Miyu. Miyu is mysterious and reserved, whereas Yui is plucky and emotional.
Ill Girl: Subverted. Peple think that Yui has severe anemia, but the truth is that her Guardian powers have just awakened and, since she had no real idea of what was going on, she lacked of the blood she needed. (It's not helped by how Yui refuses to drink blood from humans if she can help it, so her Battle Butler Nagi gives her his blood instead.)
Stepford Smiler: While taking to her sempai Shouji and her friend Kyouko, Yui acts like a Genki Girl and a Shipper on Deck for them both. In reality, she's thinking of how she won't be able to keep up with them.
Weak, but Skilled: Sorta. She wins her first fight via relaying on trickery and pure sheer pluck.
Thou Shall Not Kill: Sorta, as for quite a while doesn't like the idea of feeding from humans. Nagi then lets her feed from him.
Un-Person: After the funeral of Yui's grandmother, it's strongly implied that Miyu and Larva erased Yui's presence from the memories of her few remaining friends.
Broken Bird: She's said to be a gorgeous woman "with crimson lips and sad eyes".
Convenient Coma: Self-induced. Yuki was in a Star-Crossed Lovers deal with a human, and thus she and her lover preferred to go into eternal sleep at the bottom of a magical lake that Yuki was bound to. (Said man was the stepbrother of Nagi, who'd become Yui's protector.)
Odd Friendship: Played with. After getting bitten by Miyu, Sayuri sorta continued her life and Miyu dropped by sometimes to check on her well-being. However, this being Miyu, her main interest was the baby still within Sayuri, Yui, whose potential she wanted to awake. (It's implied, however, that Miyu might have cared for Sayuri in her own way.)
Widow Woman: Sorta. It's all but spelled that, since her husband was a Shi, Miyu either killed or banished him and then bit Sayuri to both have her blood and relieve her from pain. People believe that he died in an accident, however.
Military Brat: Her dad shows up wearing an uniform and is referred to as "Shougakuin-sama", so it seems he's got a rather high rank. (According to Yui herself, though, he has just been promoted into it.)
Numerical Theme Naming: His name, Jirou, means "second son". It's a name usually given to the second child born in a family, if said child's a boy. (And double if the first child is a boy and his name is Ichirou aka 'first son'.)