Kojou is a vampire, the fourth primogenitor, as such he gains several abilities
Cleansing: A phenomenon that alters the laws of physics and magic, fundamentally allowing its user to warp reality.
Enhanced Vampiric Abilities: Supernatural strength, consciousness, durability, speed, agility, regenerative abilities, endurance, senses, pheromones and immortality.
As Kojou is immortal, he cannot become old or sick and will recover from any damage he receives.
Familiar Summoning: Kojou can summon twelve familiars, that act as manifestation of his vampiric powers. He gained control over them by drinking human blood.
1st Familiar: Mesarthim Adamas - This familiar is able to manipulate diamonds. It is able to disperse or scatter them like shotguns and form shields that reflect various attacks and abilities, which makes it well balanced in attack and defense.
2nd Familiar: Cor Tauri Sucinum - This familiar can manipulate both lava and tectonic plates, but it mainly attacks in close quarters.
3rd Familiar: Al-Meissa Mercury - This familiar is capable of eating space itself along with the dimension. It is able to destroy Angel-Faux Divine Oscillation barrier. This is one of Kojou's most dangerous familiars as it can even leave severed space after it's attack which may pose danger for third parties.
4th Familiar: Natra-Cinereus - This familiar is capable to render anything ethereal by producing mists. Due to the fourth primogenitor's strength, the mists are able to cover the whole island without any difficulties.
5th Familiar: Regulus Aurum - This familiar is capable of producing and manipulating electromagnetic energy. Kojou can manipulate the beam to create a force field around him. The ray is strong enough to destroy a barrier of divine oscillation and neutralize Wiseman's Blood energy beam, which was already capable of atomic-level destruction.
6th Familiar: Minelauva Iris - This familiar is capable of manipulating the laws of nature and also carries the cause and effect cutting ability.
7th Familiar: Kiffa Ater - This familiar is an intelligent-type weapon, a gigantic demon sword over 100 meters in length. This trident-like sword is capable of manipulating gravity. It can obliterate a few dozens of kilometers if swung from a high altitude.
8th Familiar: Shaula Viola - This familiar can manipulate poison and can make antidotes, as well as steal the magical power from other familiars.
9th Familiar: Al-Nasl Minium - This familiar is capable of producing and manipulating sound. It is able to create sound quakes and waves. It can tear molecules at an atomic scale by emitting high-frequency vibrations from it's entire body.
10th Familiar: Dabih Crystallus - This familiar's ability is mental and spiritual manipulation.
11th Familiar: Sadalmelik-Ablus - This familiar is capable to revert phenomenon to its original state which is nothingness. Due to this ability, Kojou is able to recover from any kind of injury including decapitation as shown in the series. It is able to erase conceptual existence.
12th Familiar: Alrescha Glacies - This familiar can manipulate water and lower the temperature below absolute zero.