Kohaku (琥珀,Kohaku?, literally meaning "Amber") formerly known as The White Tiger (白虎,Byakko?) is a companion and contracted beast of Touya on his journey. She is one of the Four Divine Beasts and also the leader of the Demon Beast.
Kohaku's true form is that of a large White Tiger. After Touya voiced his uncertainty of walking with a tiger, Kohaku took on the appearance of a small white tiger cub which is considered cute by the female characters.
The White Tiger, The White Emperor (白帝,Byakutei?) which later known as, Kohaku, is one of the divine beast that can manifest in the world once every few decades or centuries, unless they are being summoned by human .
Kohaku was accidentally summoned by Touya Mochizuki when he was learning the summoning spell under supervision of Yumina Urnea Belfast. At their first meeting, Kohaku released her Intimidating Aura which froze both Yumina and Silver, her silver wolf summon. However, Touya, who has high magic level than Kohaku, was unaffected by her sharp and penetrating aura. Felt uneasy with the situation, Touya asked Kohaku to release both Yumina and Silver from her aura. Touya then immediately asked Kohaku to become his servant following the releasing of the suspense. After briefly expressing her resentment toward Touya's request, she felt an extraordinary divine spirit that residing inside Touya's body. Because of her curiosity, Kohaku allowed Touya to become her master only if his magic was superior enough for her. Touya who had been blessed by God with tremendous amount of mana, he was able to knock Kohaku unconscious. Subsequently, Touya recovered Kohaku using [Cure Heal] spell. On keeping with her promise, Kohaku then accepted Touya as her master and granted "Kohaku" as her name. She later asked Touya Whether he had spend most of his mana. To his surprise, Touya had hardly spend his mana after releasing a cascade of mana, Kohaku then asked Touya if she could incessantly manifest in the world. He would agree to her request only if she could working on her appearance. Being agreed to do so, Kohaku then changed her appearance from menacing white tiger to a cute white tiger cub.
Intimidation Aura: She is able to release suppressing aura that render all individual, which have lower magic level in respect to the divine beast, becomes immobile.
Long-Ranged Telepathic Communication: She is able to make telepathic communication with her master and among the divine beasts regardless the distance. She also able to include other people into this communication line.
Form Transformation: She is able to change her menacing true form appearance into cute young beast form (Child Form) and back as she pleased.
"Master Mochizuki Touya. By my judgment, there are none I have ever crossed paths with more suitable for the role of my master than you. I would be honored if you were to form a Master-Servant pact with me." - Kohaku accepting Touya as his master.
Her name, Kohaku (琥珀), which is a Japanese word for the gemstone Amber, is actually a combination of 3 different Japanese words which are Tiger (虎 Tora), White (白 Shiro), and King (王 Ō).
Based on the Chinese characters (漢字 Kanji), her name can be also translate as "a white tiger that stands next to the king".
Touya Mochizuki had mistaken Kohaku as a male before it was revealed that Kohaku is in fact a female tiger
She is the only divine beast which direct summoning spell is unknown.