Gensōmaden Saiyuki Series by Kazuya Minekura

It was a time of chaos, when Heaven and Earth were as one, and humans and demons - the youkai - lived together in peace. The foundations of civilization and religion were raised and reinforced in this land of Togenkyo, the paradise known as Shangri-la.But now, a great evil threatens harmony in this great land. Far to the West, in India, someone is attempting to resurrect the youkai lord Gyumaoh by mixing human science with youkai magic... moreIt was a time of chaos, when Heaven and Earth were as one, and humans and demons - the youkai - lived together in peace. The foundations of civilization and religion were raised and reinforced in this land of Togenkyo, the paradise known as Shangri-la.But now, a great evil threatens harmony in this great land. Far to the West, in India, someone is attempting to resurrect the youkai lord Gyumaoh by mixing human science with youkai magic. This forbidden practice has created a Minus Wave of negative energy that is spreading across Shangri-la, poisoning the souls of the youkai and turning them into mindless monsters. The only hope lies in four legendary heroes: Genjyo Sanzo, a high priest with low morals; Son Goku, the hungry and mischievous Monkey King, just released from 500 years imprisonment; Sha Gojyo, a water sprite with an addiction for good smokes and bad women; Cho Hakkai, the legendary demon slayer, and his transforming dragon Hakuryu. To save Shangri-la, these unlikely companions, united by fate, must travel together ... INTO THE WEST! Having been assigned by the human elders the mission of stopping a mystical plague that has afflicted the Youkai with madness, Genjyo Sanzo assembles his team of Youkai warriors, desperately hoping that the disease will not affect them. He sets up qualifying tests that will help him determine the loyalty and worth of Cho Hakkai, Son Goku and Sha Gojyo. The team then journeys west to rid the land of madness. less

Continuing their journey west and leaving a trail of dead Youkai in their wake, Genjyo Sanzo and company come upon a young woman who has quite a tale to tell.

In the midst of battle with Sanzo and his team, a cursed human by the name of Rikudo impales the human leader, as he tries to protect Goku. In the melee, Goku's Youkai power limiter, the device that keeps his Youkai madness from taking over his soul, shatters, sending Goku into a violent rampage that yields for neither friend nor foe.

The mysterious fortune-teller Chin Yisou takes great pleasure in pushing Hakkai's psychological boundaries, and Hakkai is frightened to find his bloody past nipping at his heels. When Chin Yisou starts targeting Sanzo and the others, our heroes find themselves not only fighting against him, but against each other.

Violence drew them close, but something far more powerful kept them together. The story of how Sanzo, Goku, Gojyo, and Hakkai met is revealed at last.

With poison coursing through his veins, Sanzo's life dwindles as Goku and the others fight to discover a way out of their desert prison. Although Kougaiji offers a solution, there's a catch - Goku must first defeat him in combat! Goku's desperation grows as Sanzo's health rapidly fails, but there's no divine intervention if Goku loses control this time. Will Goku put Sanzo's life above everything...and everyone?

A set of twins barge in our heroes, one which is transformed into a monster. While Goku and Hakkai are sucked into the twin's magical gourd, Sanzou and Gojyo set off a hunt for the twin. They find that the demon twins escaped from their village and were taken under the wing of God, a mysterious figure who granted them whatever they wanted.

Sanzo, Goku and Hakkai are out to find "God"--and Gojyo. At the same time, Gojyo climbs a seemingly endless stairway to heaven and is assailed by a very maternal monster. The gang finally catches up to Gojyo, and as luck would have it, they've also found "God." But this dangerous deity is no ordinary opponent, and the quartet must get serious before they get crushed.

Feeling down in the dumps about losing in the battle against "God", Goku attempts to raise everyone's spirits with a game of Mahjung (sp?). He wins match after match until he scolds them all to snap out of it and shape up, leading to them playing a whole day straight of the game. Ready for another round, the gang approaches "The God's Castle", where they run into a bit of trouble with talking toys, before finally reaching "God". They kick major ass and succeed in beating him in the end... moreFeeling down in the dumps about losing in the battle against "God", Goku attempts to raise everyone's spirits with a game of Mahjung (sp?). He wins match after match until he scolds them all to snap out of it and shape up, leading to them playing a whole day straight of the game. Ready for another round, the gang approaches "The God's Castle", where they run into a bit of trouble with talking toys, before finally reaching "God". They kick major ass and succeed in beating him in the end. There is a flashback of when Sanzou was younger and had a run-in with a young "God", who was a disciple to Ukoku Sanzou Houshi, a very powerful and wise monk. With the "game" over, the castle around them collapses, but they manage to escape. Amongst the ruins, Ugoku appears and picks up "God"s (I think his name is actually Kouryuu) fallen monk hat and announces that he's ready for another "game". Our heroes drive off into the distance, back to their usual bickering selves, but the story is far from over... less