Rokugan's Spirit Realms in Planescape

I've done a bit of thinking and have applied some of the 3e Manual of the Planes planar traits to Jigoku and the Shadowlands. Here is what I've come up with so far.

The Shadowlands

Normal Gravity
Normal Time
Finite Size
Alterable Morphic
No Elemental or Energy Traits
Strongly Evil Aligned and Mildly Chaos Aligned
Impeded Magic - Any divine spell that calls upon the power of the kami (that is, any spell from the Shugenja spell list that is not maho) is impeded because of the natural tendency of the kami to avoid Jigoku's corrupting touch. In addition, any shugenja wishing to cast a divine spell in the Shadowlands runs a risk of attracting a kansen (a Tainted kami) and acquiring a Taint score. All arcane magic, all divine magic that does not call upon the kami, and all maho function normally in the Shadowlands.
Tainting: See the Rokugan campaing setting book for information on how the Tainting mechanics work in the Shadowlands.

The mechanics for the Impeded Magic are something I might work out more concretely at a later time. This list was put together on a sort of "spur of the moment" thing. At first glance, the biggest things I'd consider changing are adding a mildly negative-dominant trait and making it mildly evil-aligned instead of strongly evil-aligned. The negative dominant would exist because on occasion, the dead may just suddenly pop up and start roaming around. There is a story where Otaku Kamoko basically does just that -- She gets killed, then she stands up and kills her killer.

The Abyss, where the heart of Jigoku is located, is listed as mildly evil-aligned. However, I gave it a strongly evil-aligned trait because Jigoku is driven to corrupt. The spirit realm itself is trying to corrupt everything in the Celestial Order with a fervor that borders on sentience. The feeling I get of Jigoku's drive is one of much more profound purpose and will than the Abyss as a whole, and so I made its evil trait more powerful.

Finally, I might consider impeding all divine magic in the Shadowlands that is good- or law-aligned or from deities that are good- and/or law-aligned.

Jigoku

Normal Gravity
Normal Time
Infinite Size
Alterable Morphic
Mildly Negative-Energy Dominant
Strongly Evil Aligned and Mildly Chaos Aligned
Limited Magic: The kami have an intense hatred and fear of Jigoku and avoid it entirely. Spells that draw upon the power of the kami do not function in Jigoku. Therefore, a shugenja cannot cast divine spells from the shugenja spell list while in Jigoku.
Impeded Magic: Jigoku is an extremely jealous realm. It especially despises all that is good and virtuous in the universe and actively seeks to tear it down into corruption. Any cleric of a good-aligned deity who attempts to cast a spell must make a Spellcraft check against DC 25 + the level of the spell to cast. If the spell has the Good descriptor, add 5 to the DC.
Enhanced Magic: Jigoku is the land of evil and the origin of maho, evil magic. All maho spells cast on Jigoku are enhanced and affected as if cast with the Empower Spell. Enlarge Spell, and Extend Spell metamagic feats. This does not change the level of the spell in any way.
Tainting: Jigoku hungers to corrupt everything. Anything that is not corrupted that enters Jigoku runs the risk of being overcome by the Taint and becoming Lost. The base save DC for resisting the Taint starts at 20, rather than 10 as in the Shadowlands. Jade carried into Jigoku to protect against the Taint becomes corrupted at twice the rate it corrupts on the Shadowlands. See the Rokugan campaign setting book for more information regarding Tainting mechanics.

Again, I might consider adding an impeding trait to lawful deities and lawful spells. The thing that makes me hesitate is that the latest Dark Lord of the Shadowlands, Daigotsu, strikes me as a Lawful Evil alignment rather than Chaotic Evil.

Maho is really as much divine magic as regular Rokugan magic is. The source is just different. Maho uses blood as the focus/component for its spells, but the source of maho is Fu Leng -- or sometimes Jigoku itself In fact, the Phoenix (and I think the Unicorn as well) hold knowledge of "pure blood magic" that uses blood similar to maho, but is a pure form of magic. Arcane magic in the form of wizardry or sorcery doesn't exist on Rokugan, except among the Nezumi.

I like the ideas you have presented with regards to enhanced maho and impeded shugenja magic, and I might use something similar to that. But all forms of magic in Rokugan, maho or otherwise, is divine. The only exception is Nezumi name magic, and the ratling nameseekers use the sorcerer core class. I realize OA says that maho-tsukai use arcane magic, but based on the actual lore of the maho of Rokugan, I think that's a flawed concept.

I disagree with a lot of the presentation of Rokugan as described in OA. Some of it is outright wrong. For example, the opening text for the Shadowlands says that the Shadowlands were created when Fu Leng fell from Heaven and broke the earth, creating a portal to Gaki-do. This isn't just flawed, it's outright wrong. The Festering Pit, where Fu Leng fell, is a portal to Jigoku, not Gakido. The two are very different and distinct realms.

Now that you mention that, I think OA put the arcane vs. divine in there simply to make the Shadowlands compatible with OA in general -- I personally dislike that they put all of these Eastern elements in and then threw Rokugan as the main setting for them. For example, shaman and wu jen classes don't exist in Rokugan. The only spellcasting class (non-maho) that humans can take in Rokugan is shugenja. But it seems to me that it's difficult or impossible to learn to use maho magic without either first being a shugenja (virtually all of the most powerful bloodspeakers and maho-tsukai were shugenja before their fall) or without guidance from Jigoku (as was probably the case with Iuchiban). Either way, it suggests the caster requires divine influence. Jigoku is virtually as much of a sentient force as any deity, so I see cause to overrule the arcane enhancement in a strictly Rokugan sense. If using general OA, I guess the presentation in OA works fine.

That's true, but I think it's something they should have caught, given the real legend behind the Shadowlands. At any rate, I don't really know how much attention the Spirit Realms got pre d20 Rokugan. I know they've existed since Rokugan was conceived, but I never did get much access to the d10 system books. I can probably snoop around the game stores here and find out, though...