When playing in or running an isekai campaign, an element of the story is just how the characters arrived in this strange, new environment. How the PCs arrive determines much about how the world operates, how people treat them, what the characters might already know about the world, and whether the characters get to play as idealized versions of themselves or as someone else entirely.
Methods for Getting There
While the methods for arriving on another world from Earth are limited only by the GM’s imagination, here are some common methods anime and manga stories use.
The PCs are summoned to their new home with the aid of a powerful spell or magical artifact. Typically, the PCs arrive in their own bodies, but they might appear in a completely new form due to the specifics of the summoning.
Most of the time, the PCs are summoned for a specific reason, such as slaying a terrible dragon god ravaging the empire. However, the PCs might have accidentally or mistakenly been summoned by someone expecting a completely different group of people.
Portal to a New World
A method found not just in anime and manga but also stories such as Alice in Wonderland and The Chronicles of Narnia, this method involves the PCs passing through a portal to another world. The shape and location of the portal could be anything, but symbolism calls for some door or opening to be breached, accidentally or on purpose.
A crucial decision for this method is whether the portal stays open after the PCs pass through or it closes behind them. Traditionally, the portal closes so that PCs are driven toward action. If the portal remains open however, it allows PCs (and possibly their enemies) to step back and forth between worlds, for good and ill.
This method occurs when the PCs die on Earth only to be reincarnated into different bodies in another world. This can mean starting life from scratch as a child in the new world or appearing in the body of a recently dead creature. The PCs might also appear in their own bodies, having been reincarnated in the new world thanks to divine providence (or stupidity).
Depending on the nature of the reincarnation, PCs may only have vague memories of their time on Earth and lack skills from their previous lives, making this method a simple choice for GMs wishing to run a traditional-style 5E or Tales of the Valiant roleplaying campaign.
Trapped in a Game
A group of friends playing an MMO finds themselves transported mentally or bodily into the game world. Again, the players might appear as themselves, but more often, they appear in the bodies of their characters. The explanation for their appearance is a mystery that they must uncover later.
This method is particularly suitable for higher-level PCs (10th and above) because they are known in the game world. This doesn’t always need to be the case, however. It can work equally well for beginner PCs.
You can even combine methods. For example, a magical summoning ritual might involve the PCs’ souls being transported into the bodies of freshly sacrificed criminals or the PCs might become trapped in a video game after passing underneath a store sign advertising the game.
Not all PCs need to arrive in the same way, either. One PC might be reincarnated while another is summoned. However, some consistency should be maintained between PCs’ methods of arrival and how this affects their abilities to maintain game balance.
Most methods of transporting the PCs to another world are intentionally mysterious and not meant to be reproduced by the PCs. However, there’s more fun available to players who can make choices.
The following two rituals are powerful, hard to find, and only cast in dire circumstances. Both are probably best offered in the late stages of the campaign or as they seek to replenish their ranks with people from their own world.
Note that these two rituals use Tales of The Valiant system notation, giving you spell source rather than classes that can cast them. It also refers to spells as “circles” instead of “levels” as a way to differentiate the terms.
8th-Circle Divine (Necromancy, Ritual)
Casting Time: 1 hour
Components: V, S, M (a dead body anointed with special herbs and oils worth 5,000 gp that are consumed in the casting)
You transfer the soul of a creature who has died in another world into the dead body of a creature in your world. This ritual works on the body of any creature except for a Celestial, Construct, Elemental, Fiend, or Undead, provided that the body is relatively intact.
The soul retains its personality and alignment but gains all its new body’s physical traits and abilities. It can call on its memories and use them as it sees fit. This ritual also allows the newly transferred soul to understand Common and any language its new body previously had access to.
A creature brought back to life by this ritual possesses the statistics of the relevant creature (such as that of an owlbear) or class levels, as appropriate, though you can never transfer a soul into a body whose level exceeds your own.
9th-Circle Arcane (Conjuration, Ritual)
Casting Time: 1 hour
Range: 30 feet
Components: V, S, M (a magic weapon placed within a magic circle inscribed with powdered silver worth 1,000 gp. The magic weapon is consumed in the casting)
You summon a hero from another world. The hero gets no saving throw against the spell but is not trapped within the magic circle and is free to act as it sees fit.
When you cast the spell, you determine what sort of hero you summon and their relevant skills and abilities depending on the type of magic weapon you place within the magic circle. For example, a magic longsword calls upon a hero capable of wielding such a blade, while a magic staff within the circle would call upon a hero adept at wielding magic.
This spell can never call a hero whose level exceeds your own.