There might be doubles in what I put. I’m too lazy at the moment to go through them all.
Demon x Demon
Demon x Human
Demon x Angel
Doctor x Patient
Elemental x Elemental
Warrior x Mage
Master x Apprentice
Elder Vampire x Elder Vampire
Elder Vampire x Newborn Vampire
Newborn Vampire x Newborn Vampire
Band Member x Non Fan
Knight x Squire
Prince x Servant
Prince x Prince
Prince x Commoner
Prince x King
Prince x Vampire
King x Servant
King x King
King x Commoner
King x Vampire
God x Mortal
God x God
Mage x Commoner
Master x Slave
Student x Student
Student x Teacher
Teacher x Teacher
Twin x Twin
Twin x Twin x Someone else
Priest x Demon
Priest x Vampire
Boss x Secretary(Yes, there are male secretaries)
Virtual Avatar x Virtual Avatar
Ghost x Living Person
Vampire x Servant
Upperclassmen x Underclassmen
Rich Kid x Poor/Middle Class Kid
Class Clown x Quiet Kid
Player x Quiet Kid
Tutor x One being Tutored
Popular Guy x Quiet Kid
Delinquent x Top of the Class
Dropout x Kid from Rich School
Magical Pet(Animal to human) x Owner
Life Long Friends
Detective x “Bad Guy”
Dream Guardian x Nightmare Guardian
Alien x Human
Death x Mortal
Creator x Creation
Cyborg/Android x Human
Teammate x Teammate
Dark Half x Light Half
Band Member x Manager
Band Member x Producer
Outcast x Non Outcast
Outcast x Outcast
Mad Scientist x Normal Person
Mad Scientist x Assistant
Necromancer x Elf
Elf x Mortal
Cousin x Cousin
King x Assassin
Prince x Assassin
Knight x Lord
Accidental Hero x Fated Protector
Assassin x Target
Warrior x Commander
Rivals
Vampire x Human Descendant
Author x Editor
Music Instructor x Student
Vampire Hunter x Vampire
AI (Artifical Intelligence) x Online Game Player
Alien x Government Agent
Alien x Human
Alien x Human Spaceship Captain
Alien x NASA Astronaut
Alien x Scientist
Android x Scientist
Angel x Fallen Angel
Angel x Religious Figure
Author x Plagarist
Artist x Model
Asylum Patient x Private Investigator
Bartender x DJ/Dancer/Stripper
Brother x Brother
Choir Star x High School Choir Teacher
Circus Performer x Circus Guest
Creation x Scientist
Drawing Come To Life x Artist
Fallen Angel x Angel/Demon
Fan x Famous Singer/Athlete/Actor
Florist x Customer
Foster Brother x Brother
Ghost x New Home Owner
Ghost Hunter x Ghost/Demon
Government Official x Foreign Spy
Hairdresser x Customer
High-Ranking Mafia Man x New Mafia Recruit
Incubus x Orphan
Incubus x Priest
Insane x Insane
Insane x Sane
Inventor x Priest/Religious Figure
Jock x Freak
Keyboardist x Singer
Lawyer x Doctor
Master x Servant
Merman x Scientist
Merman x Shipwrecked Survivor
Merman x Wealthy Businessperson
Model x Model
Murderer x Investigator/Cop
Naga x Collector of Rare Animals
Naga x New World Explorer
Naga x Plane Crash Survivor
Politician x Journalist
Prostitute x Client
Prostitute x Unhappy Spouse
Reaper x Dying Person
Rich Customer x Waiter
Runaway x Businessman
Shapeshifter x Human
Shapeshifter x Scientist
Spy x Government Agent
Step-Brother x Brother
Step-Son x Step-Father
'Stolen Property' x Thief
Terminally Ill Patient x Nurse/Doctor
Test Subject x Scientist
Therapist x Insane
Young Genius x Jealous Family Member