I was leafing through Magic in the Shadows, mainly because I might have a player who'd like to play some asian-influenced mage. She prefers Shintoism..and now I'm at a loss at where to look if that has been already coverec in the rulebooks somewhere.

Anybody got some information on stuff like that and where I might find some rules?

Can't help you with specific rules. Can help you with background:

The About overview
Shinto on-line network association
Sacred Texts (Shinto page)

Here's something...
Shinto Rituals

Just use the same rules on magic, and change the rituals instead.

Shinto Magic, pg. 26, Magic in the Shadows. That should just about cover it in terms of canon rules suggestions.

Yes, that page will give you some ideas for "flavorizing" teh character's magical activities. As far as I can tell, they would just summon regular nature spirits like a shaman from another tradition/culture, and maybe be able to summon Ancestor Spirits at your discretion.

Shinotism also uses the classic "Paper magic" often used in anime, where incantations are on strips of paper stuck on walls as wards or stuck on beings to control, empower, or paralyze them.

Wouldn't you run a Shinto based mage as a shaman will different perceptions of how the spirit world works?

Minor nature Kami after all could simply be represented by simple spirits, and more major Kami could be represented by Great Form spirits, courtesy of Invoking.

As for the personal totem, the nature totems (particularly Sun and Mountain) would work well, as would the Archetypes and some of the mythical totems.

My opinions on the matter at any rate (which means they're probably wrong )

I played a shinto type character, just used the ancestor shaman rules. No troubles here.

Doh! *smacks own forehead*

Yeah, I admit, I'm guilty of not reading through the whole book yet...thanks for pointing that chapter out to me.
I have to admit, I like the broadening of concepts in Magic in the Shadows

As specific rules go... I, too, played a Shinto Miko in Shadowrun. Rules-wise, she was effectively a shaman with a patron Kami, granting her totem bonuses. In lieu of a shamanic mask, glowing characters would appear in the air around her as she cast. Generally, characters like that would not be able to summon Spirits of Man, and would be able to summon ancestor spirits instead. In her particular case, if your player wants to have a particular patron Kami, select an appropriate totem or idol and adjust to an asian feel.

Most of the differences are flavor, and not rules. For example, instead of a Lodge, she had a portable shrine she set up. For expendable foci, she used the paper charms popular in anime. Same rules, same availibility, different look.

You don't need to bend any actual rules, just give her a few colorful special effects, and you're good to go. And don't forget to encourage her to do her part-- have her read up on Shinto chants, for example, and encourage her to pick up that as a knowledge skill. If she later learns Centering, it'd be very appropriate. While I wouldn't precicely enforce it, I would highly suggest that she also take a Religion: Shinto knowledge skill, at least at a 4 or better, and 7 is preferable.

Good information on Shinto here. However, in addition to the traditions surrounding Buddhism and Shinto, another Japanese mystical tradition is that of "shugendo", which embraces a more elemental worldview, something any L5R fans out there are doubtless familiar with. This elemental form of Japanese magic has much in common with wuxing, and would account for the seemingly unique system reputedly practiced by the infamous ninja clans of Japan. Here's a quick overview:

Magical Info: Shugendo
Traditional Japanese form of wuxing based on the five elemental "rings" of Fire, Water, Earth, Air, and the Void. Practicioners of shugendo (called "shugenja") gain the ability to summon ancestor spirits from the Void ring, but, as there is no Wood element in ring magic, they must choose between summoning manitous and summoning spirits of Man.
Fire: Combat and salamanders (opposes Void)
Water: Health and undines (opposes Fire)
Air: Illusion and sylphs (opposes Earth)
Earth: Manipulation and gnomes (opposes Water)
Void: Detection and ancestor spirits (opposes Air)

Spell-learning and summoning function identically to wuxing, but have stylistic differences. For instance, paper-based libraries are typically made up of scrolls, rather than tomes. Meditation is central to the practice, and, in the ninjutsu tradition of shugendo, kuji-kiri (a form of gesture) is a common geas. Just thought I'd toss it out so the thread wasn't ALL Shinto-related

Hmmm, nice variant of L5R magic, Blackfeather. Thanks for spiking my interest in that direction, actually I guess my player would prefer to stay a more traditional Shinto miko instead of a yamabushi...but their traditions would make a great contact to a magical group, and their ascetic lifestyle and philosophy a great backdrop for an ascetic initiation...or an ordeal