Rosencrantz is the second member of the Genma Triumvirate. He also inherits the title of 'The Scientist' and is a character and boss enemy, encountered in Onimusha: Dawn of Dreams.
From the very little of what we know of Rosencrantz, he was the most precise and malicious scientist in the Genma race at the time. It is thought that because of this, he even outwitted Guildenstern. Rosencrantz became a member of the Genma Triumvirate after he was promoted by Fortinbras. It was thought he was promoted because he was the most intelligent Genma at the time.
As one of Fortinbras' most trusted servants, he was charged with advancing the Genma to a new dawn of age, often performing experiments on both Genma and humans alike. In the process, however, the strain and pressure that this brought on his mind caused Rosencrantz to go completely mad. Despite this, he still got some impressive results from his experiments and research, pleasing Fortinbras greatly.
When the great war came between the God of Light and the God of Darkness, Rosencrantz was hunted down and destroyed, and was banished along with Fortinbras to the deepest reaches of the netherworld.
Rosencrantz in Dawn of Dreams
In Dawn of Dreams Rosencrantz is possessing Roberto Frois's adoptive father, Luis Frois. Luis was a Porteguese priest and missionary, who arrived in Japan just after Nobunaga was defeated and Hideyoshi unified the country. He was ordered under Mitsunari to do research on the Genma. In the process, however, the spirit of Rosencrantz took control of Louis and he suffered for many years under the strain of him.
It was during these years that he then began to experiment with the Genma on Roberto's friends. Roberto had lost many friends in the process, and vowed revenge. He did not realize, however, that it was actaully Rosencrantz and not Luis that had killed Roberto's friends. Luis eventually dies along with Rosencrantz at the Shimabara Research facilty in the explosion, when the second Dark Stone is destroyed. He is finally freed from Rosencrantz in the process.
Rosencrantz is revived by the essence from the omen star, however, and makes an appearance at Osaka in his true Genma form. His true form is revealed as a giant Genma fly that has the ability to harness energy at will. He is finally killed by Roberto.