Reincarnator

Reincarnated Ones 「転生者, Tenseisha」 (Reincarnates or Reincarnators) are those individuals that have departed from their bodies and have been reborn into this world. There are two types of reincarnators: those that died and were reborn into the same world (Inhabitants)「世界人, Sekaijin」, and those that died (or experienced a dimensional rift) from a different world were reborn here (Otherworlder)「異世界人, Isekaijin」.

Reincarnated Inhabitants
Reincarnated Inhabitants often have strong individual wills and abilities to be successful in reincarnation. Depending on the circumstances, the reincarnated person may or may not have their original memories. Those who do, end up gain additional knowledge or power compared to their previous state. This may be because since their souls have resisted the flow of the world (all life dies in the end) they are rewarded as being greater that they originally were.

In the case of Humans, they may sometimes achieve an evolution to a Sage and then, in even rarer cases, into a Saint. It is also possible for a person to die and not fully reincarnate into a physical body but remain as a spirit, such as Venom who turned into a Demon in the spirit world. (Disclaimer: It is unclear if Venom is an Otherworlder or an Inhabitant as it is not clearly stated, but there is no doubt that he's a Reincarnator.)

In the case for monsters such as the True Dragons, they are considered dead only if their cores are destroyed, otherwise, as beings of mass energy, they can easily regenerate as their magic returns. However, after they die, they will eventually "respawn" or be reborn into the world again somewhere else, albeit, without their memories. This is because the "world" only cares about the existences of the "dragons" as "natural" existences and not "individuals."

List of Known Reincarnated Inhabitants

 * Rudra Nam Ul Nasca
 * Gadra
 * Venom
 * Velgaia

Reincarnated World Travelers
Reincarnated World Travelers also need powerful wills or some form of remnant thought (something like dying wishes), whether that's a conscious or subconscious wish. Unlike Reincarnated Inhabitants, it's possible for people who have incredibly powerful wills but still not reincarnate into this world, meaning that the process is either random, or there is some compatibility issue.

Regardless, those who have reincarnated from a different world, because of their souls having to resist the pressure of traversing into a different plane of existence or reality, the reborn individual will often times acquire one or more Unique Skills and/or several other abilities and resistances.

Usually, most Otherworlders are reborn as Humans, the same as their previous life. This means that it was an incredibly rare and unique phenomenon for Rimuru to reincarnate as a monster.

List of Known Reincarnated World Travelers

 * Rimuru Tempest
 * Leon Cromwell
 * Chloe O’Bell (Later summoned to a timeline)
 * Yuuki Kagurazaka
 * Hinata Sakaguchi