Otherworlder

Otherworlder (異世界人), refers to humans that come to the Central World from other worlds.

Summoned
Summoned (召喚者) are the most common type of otherworlder, brought to the central world through summoning rituals. It's a very dangerous process for the summoned, as they're exposed to massive amounts of magicules when crossing over the boundary between worlds. Only those that bear a strong enough soul can withstand the journey and endure having their bodies obliterated and rebuilt, taking in a large amount of energy and becoming semi-material. From the massive energy taken in by the summoned, Unique Skills and other special abilities are born out of their desires, making them a powerful asset to any human nation.

Summoned are typically recruited as weapons against monsters and are also expected to serve as champions and even heroes for humanity, with most of them serving as bodyguards for kings and nobles. For this reason, a locking curse is sometimes placed on the soul of the summoned, bending them to the will of the summoner and preventing them from fleeing.

There are very few forces capable of summoning otherworlders due to the effort and cost involved. Even meeting the ideal conditions for a proper summoning, the chances of successfully calling an otherworlder is less than 1%. There's also an inconvenient cooldown period spanning decades which prevented it from being used continuously. Due to the knowledge propagated by Leon Cromwell, however, a less strict and simplified variant of the summoning ritual was eventually born. It came with a higher success rate and could even be used continuously, but the consequences were that it resulted in children. These children usually had no skills and were left with only their vast magical energy, which, having failed to be converted to skills, caused them to perish within five years. Upon Rimuru becoming a Demon Lord, this practice became outlawed out of fear of incurring his wrath.

Visitor
Visitor (来訪者) or Otherworlder transported by accident (偶発的にやって来る異世界人), refers to otherworlders that arrive by sheer accident. There is no clear cause or pattern known for why this happens, but in general, it's considered a one-way street and the phenomenon is not known to happen in reverse.

Among the three ways for otherworlders to appear, this is the least dangerous. The only real danger is a lack of a fixed target location in the beginning, so it's possible for the vistor to suddenly find themself in hostile lands. However, if that hurdle is cleared and the visitor manages to acclimate themselves to life in the central world, then the greatest danger has passed. Unlike summoned, visitors are not subject to any enslavement and thus enjoy greater freedom; likewise they are not guaranteed to obtain a unique skill. Visitors tend to be comparatively weak to summoned, like in the case of Yoshida, though there are exceptions such as Hinata Sakaguchi who managed to obtain two unique skills upon arrival.

Reincarnated
Reincarnator (転生者) or Transmigrant, refers to individuals that arrive with no body and just their mind, being reborn as an inhabitant of the central world. Reincarnation tends to happen randomly. Although there are those among the reincarnated who still remember their past life, to have reincarnated from a different world is exceedingly rare. Moreover, one would normally be reincarnated as a human. For someone to be reincarnated as a monster, and from magical energy itself, is something that remains unheard of. The only known example of this is Rimuru Tempest.

Reincarnated

 * Rimuru Tempest
 * Agera
 * Venom
 * Mariabell Rosso
 * Mujika

Visitors

 * Hinata Sakaguchi
 * Kaoru Yoshida
 * Leon Cromwell
 * Masayuki
 * Tatsuya Kondou
 * Byakuya Araki
 * Bernie
 * Arios

Summoned

 * Shizu
 * Yuuki Kagurazaka
 * Chloe Aubert
 * Alice Rondo
 * Kenya Misaki
 * Gale Gibson
 * Ryota Sekiguchi
 * Folgen
 * Shogo Taguchi
 * Kyoya Tachibana
 * Kirara Mizutani
 * Glenda Attley
 * Shinji Tanimura
 * Mark Lauren
 * Zhen Liuxing
 * Lucius
 * Raymond
 * Orlia
 * Alrose

pt-br:Viajante Mundial