While not doing Manga professional but usually putting his focus on Visual Novel he did try his hands as an Author of the Manga Adaption of the legendary Umineko Series.
Serialized in: Gangan Joker (2008)
Genre: Action, Drama, Horror, Mystery, Psychological, Romance, Shounen, Supernatural, Tragedy (Note it says Shounen though it really shouldn't be)
International Release: None.
Online Status: Ongoing
Age Ranking: It is featured in a Shounen Magazine, however don't ask me why as it's clearly Seinen.

The Summary:
Quote Quote:
In 1986, between October 4th and 5th, members of the Ushiromiya family gather on the secluded island of Rokkenjima to discuss the division of the family's massive fortune upon the impending death of the family's head, Kinzo.

However, when a typhoon traps the eighteen people present on the island, six people are mysteriously murdered. The remaining people struggle to survive as the murders continue, supposedly by the will of the legendary Golden Witch, Beatrice.
What Ryukishi has created is an absolute unique Murder Mystery which has not a single rival in terms of Complexity, not even against Arthur Doyle or Agatha Christie.
We the readers are the detectives, its up to us to find the truth behind the incidents that occur, which is where the story shines.
How is a reader supposed to explain that the Killer turned into a swarm of butterflies?
How is a reader supposed to explain that with 18 people present, the killer being among them yet at the same is not?
These are the kind questions we are faced and its up to us to solve them, in a very unique fashion such as a set of rules.
Everything written in red is the truth, however, just because it's truth doesn't mean it's an answer, so turns a room that appears normal into an absolute perfectly locked room or that a person was killed by the Culprit that is non-existant yet is among the 18 on the Island.

Ryukishi really put his entire heart into this and what comes out is a Murder Mystery that is unparallelled to the point where one can only regard him as a Genius on the level as Doyle and Christie at least in my opinion.