In early days, as Dean Meistre he was a young boy with slightly tanned skin and short silver hair like all Shiroganes. As he grew into a young adult he had black hair that became longer and developed into curved spikes, his eyes remained silver, however. In his older days his black hair is shorter, almost similar to that of Shoji. He also shows a more middle-aged appearance with more wrinkles.
Sadayoshi shows himself as a polite, somewhat playful and friendly man in public. In truth and being the next incarnation of Bai Jin, he retains his worst traits, namely his psychopathic obsession with Francine and their look alikes, his complete disregard for human life and anything that doesn't benefit him, and his manipulative and treacherous nature.
He will use anything and everything to achieve his purpose of being loved by the image of the woman he set his sights on, no matter how underhanded or bloody he has to go to do it. At this point he has become far more self-entitled and selfish, as he stopped thinking of Angelina as a human being after she got pregnant of Shoji's child, simply reasoning she was worthless for not loving him.
After Bai Jin dissolved himself into a puddle of Aqua Vitae and kidnapping a young boy for him to drink in order to transfer his memories, was thus the man who came to be known as Dean Meistre be born. Continuing on his quest to find the Francine doll in order to retrieve the hair sample from the true Francine to recreate her as many times as needed so she would love him, he travelled back to Quiberon.
On the france town he met Angelina the niece of Francine and a Shirogane. Introducing himself as Dean Meistre, Angelina presented him with Lucille thus becoming an official Shirogane. Dean seized this chance as the perfect way to gather information on the doll he made for his plans. Over time he distinguished himself as a potent Shirogane in their fight against the Automata and his focus shifted into Angelina, becoming protective and supportive of her in order to make her love him, although the two were little more than good friends.
Eventually Lucille expelled Angelina from the Shirogane order so that she could find happiness on her own. As she travelled the world and reach Japan where she met her eventual husband Shoji Saiga. Being ironically tutored by none other than Bai Jin's older brother Bai Yin into the arts of medicine, alchemy and puppetry, Saiga would start a profitable puppet company for the local populace. Dean would later reach into Japan and meet with Angelina and Shoji. Dean would then be adopted into the Saiga family as Shoji's son changing his name into Sadayoshi Saiga.
Becoming adept at the business, Sadayoshi was a close and competent man to Shoji while trying to get close to Angelina in his own way. News hit him hard when he learned that she got pregnant of Shoji, and from that moment onwards, he discarded Angelina, not even regarding her as a fellow human being. Time passed on and Angelina's daughter Eleonore was born, and suffering recurrent nightmares from the memories of the Aqua Vitae she was infused from when she was born. Thus Shoji and Guy decided it was best for her to train as a Shirogane in order to be strong enough to protect herself but hiding her real identity from the Shirogane order.
On one travel to Quiberon, Sadayoshi spotted Eleonore as she was training and became mesmerized at another splitting image of Francine and set his sights on her next. His new plan would be far more complex and involved using brain impulse theories. Posing as Shoji, he would continuously influence Eleonore with mental suggestions, making her highly susceptible to his manipulation.
The next step of his plan involved transfering into a new, younger vessel that Eleonore could love and so he had an affair with a woman who would give birth to Masaru Saiga. Masaru would play a major part into his parts. First he would make Eleonore, via suggestion, be tricked into protecting Masaru out of a false sense of gratitude to Shoji, thus creating a close bond between Eleonore and Masaru, secondly as brain activity and memories are composed of electric impulses, he would "upload" his memories into a special machine and in turn "download" those memories into Masaru, thus making Masaru his eventual 3rd incarnation and with Eleonore "forced" into loving him, and completing his mad romantical quest. Thirdly he would seize the fortunes of the Saiga group and give them all to Masaru so the multiple local puppeteer clans under the servitude of the branch Saiga families would fight and destroy one another, leaving no one to oppose him.
This plan would take him roughly 30 years to complete, between creating the necessary equipment to download himself, as well as creating puppets for his own protection and some backup measures like the Automaton Gryphon. In the case of failure he gives a key to an employee to keep and to give to Masaru.
Eventually Shoji and Guy discovered that Sadayoshi was posing as him and of his plan to use Masaru to cause infighting. Fearing the worst, Shoji requested Eleonore to come to Japan so she could protect Masaru so both would be safe. This played right into Sadayoshi's plan who at this point was all but ready to download himself into Masaru and Shoji was about to reunite him with Eleonore.
Having no more use for Shoji, Sadayoshi infected the Kuroga village with Zonapha Syndrome in order to lure Shoji. There Sadayoshi explained all his plans to Shoji starting from trying to get Angelina to himself and later Eleonore and using Masaru to become his vessel. Shoji utterly disgusted at Sadayoshi fought the madman who brought his own puppets to kill Shoji, using his new self-made puppets, Golleyemes, Captain Nemo and Jack-O'-Lantern while demanding to know where the Soft Stone is. Shoji manages to defend himself but is slowly overwhelmed and asks Sadayoshi why he needs the Soft Stone. Sadayoshi explains that while Eleonore is a Shirogane, Masaru is not, as such the latter will age more rapidly than Eleonore will thus forcing him to redo his plan time and time again to recreate the close bond suggestion, so he plans to create Aqua Vitae so that Masaru's body will age five times slower and live a long life with Eleonore.
Shoji, however, cuts his happiness short as he reveals that he had been observing Sadayoshi carefully and had learned of the laboratory to be used to download his memories into Masaru, and that he arrived late into their encounter because he torched it down before their fight. In utter disbelief he crushes Shoji's body in a fit of rage while returning to his laboratory (in truth he killed a Shoji look-alike puppet). Seeing his equipment destroyed, his plans would be delayed a few years, in the meantime and sending a letter to Eleonore he instructed her to work and wait in a nearby Circus until Masaru approached her. He would then formally adopt Masaru and seize Shoji's fortunes.
Sadayoshi then ready to download himself, drugs Masaru and kidnaps him while starting the process in his car. In the highway, Sadayoshi encounters none other than Shoji who survived his battle and with the help of the Kuroga along Guy. Shoji attacks and severs the connection between Masaru and the machine although Sadayoshi gloats that it is too late. Trying to put an end to Sadayoshi for good, the Kuroga truck reveals an massive acid tank which Sadayoshi uses to submerge himself along with Sadayoshi. Unfortunately the truck crashes and while Shoji survives albeit losing the lower half of his body, Sadayoshi is nowhere to be seen.
Secretly he survived the encounter and escaped. He then began to rebuild his body into an automaton and became Faceless, discarding his Sadayoshi Saiga persona.