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Kanji ストレイン
Rōmaji Sutorein
First appearance
Anime Debut Episode 1
Manga Debut Chapter 3

Strains (ストレイン, Sutorein) are individuals who gained power without receiving it from a King[1]


Strains' powers develop via the Dresden Slate's power, which, although sealed, still affects the Kanto region. With the Slate's power sealed, Strains were previously rare individuals, however since the Slate's power became unrestricted, more and more civilians have developed supernatural abilities.[2]



As children, all Strains and humans take a test in kindergarten that evaluates their "Induction Variation Drift", which presumably determines their thinking processes, comparing those of Strains and humans. The test contains questions from illustrations, choosing objects that are out of place in images, and other activities that test basic intelligence and special ability capacity.  

The Gold Clan appears to hold the test, and send Clansmen off to observe potential Strains for a set period of time before determining the sort of help, treatment, or detainment needed for the public's protection.[3]


All Strains have a specific 'rank'. The most common type of Strain is the common class, while the extraordinary powerfull rank is the Beta Class, whose existence are said to be one in a million, but recent studies have shown the number increase considerably. In the past, when a Beta Class strain appears, Scepter 4 must either dispatch all swordsmen or have the Blue King handle it himself. Currently, protocol regarding Beta Strains is to dispatch the Special Operations Squad, possibly along with one or two extra squads for reinforcement. The highest rank is Ex-A (extra alpha), which are the kings. Wether there’s an alpha class between hasn’t been mentioned.

Furthermore, Strains may be assigned a "level" if they are considered high-risk Strains. Known levels are Risk 3, for high-risk Strains who live peacefully, thus Scepter 4 only keeps tabs on them, but rarely have to involve themselves deeply with the Strain's life. However, for Risk 4 Strains, Scepter 4 must arrest them on sight.[4]


Scepter 4 is in charge of the registration of Strains, which to the general public is known as the Tokyo Legal Affairs Bureau, Family Registry Department, Annex 4, which registers "special foreigners". Within this registry are Strains' personal data, including current living spaces and those they live with.[5]


The abilities of Strains vary from person to person, and can be incredibly powerful or tame. The more powerful a Strain's ability is, the more likely it is for them to be classified as 'high-risk', such as Anna Kushina or Neko. It is required for Strains to be registered in Scepter 4's database, and detainment may be necessary for Strains who do not comply.

Known Strains[]

Name Status

Anna Kushina


Neko Active
Maria Yubikiri Active
Basashi Active
Tanaka Youji Imprisoned
Mogura Imprisoned
Saya Konohana Active
'Senkōki' Deceased


  1. K: Memory of Red, Chapter 3, Page 16
  2. K Return of Kings, episode 9
  3. K SIDE: Black & White, chapter two, "I am a Cat!"
  4. K SIDE: BLUE, chapter 2
  5. K -Lost Small World-, page 240