Hojo Ujiyasu, born in 1515, was the third leader of the Late Hojo Clan (not to be confused with the original Hojo clan that ruled the country during the Kamakura shogunate) and led the Clan to its Golden Age during the turbulent Sengoku Period. Considered one of the great heroes of the Sengoku Period, Hojo Ujiyasu fought wars against some of the greatest generals of the period: Uesugi Kenshin and Takeda Shingen fought constantly against him. Hojo Ujiyasu led his clan until his death in 1571, passing the leadership of his clan to Hojo Ujimasa his son.
The more apparent difference between Ujiyasu and the other great heroes of the Sengoku Period, it's his seemingly lack of ambition. That is not to say that Ujiyasu didn't harbor dreams of greater heights, but he translated those dreams in very different ways compared to most of the other Warlords. While people like Takeda Shingen, Uesugi Kenshin, Oda Nobunaga and Toyotomi Hideyoshi were always seeking to expand more and more their rule on the land, Ujiyasu dreams were maybe minor in scale: he mostly wanted his territory to be the best place to live in the country. His focus as a civil administrator was on the capital of Odawara where he lived but his reforms extended through out the entire territory under his control. Under his care Odawara soon become the crown jewel of the Kanto region and one of the most important cities in the entire country. Ujiyasu, himself, loved to walk around the city and see the growth of the city. He talked with traders and peasants asking questions about their business and generally just lazying around. Of course with this growth Odawara also became the prime target for many of Hojo's enemies. But while Ujiyasu wasn't particularly fond of battles, you should never underestimate his abilities as a General
(Ujiyasu lazying around in Odawara)
Behind Ujiyasu's peaceful demeanor there is a incredible crafty man known for his abilities as a incredibly Siege Commander. Odawara itself was sieged two times under Ujiyasu's command, first by Uesugi Kenshin that could not outlast Ujiyasu's defence and secondly by Shingen who betted on a Blizkrieng-like attack but couldn't force Ujiyasu out and had to retreat. Under his record there is also the victory on the Battle of Kawagoe, a comeback so massive that easily surpass the legendary battle of Okehazama that made Nobunaga famous. The castle of Kawagoe, which was under Ujiyasu command, was being besieged by a 85,000 army lead by the Uesugi forces. Ujiyasu only had about 5,000 men under him. During the night, Ujiyasu ordered these men to take out their armor and follow him on a night raid against the 85,000 army. The raid group, lead personally by Ujiyasu, struck hard and fast, completely annihilating the massive army.
To top it off, Ujiyasu still had the contract with one of the most deadly group in the Sengoku period: the Fuma Clan. The Contract made by Ujiyasu as a child with the famous Devil Fuuma Kotaro, made the Fuuma clan absolutely loyal to the Ujiyasu and his successors. Perharps amused by how different Ujiyasu's personality was from the rest of the other daimyos, Fuuma Kotaro, one of the greatest Ninja, that spread chaos through multiple battlefields, willingly pledged loyalty to him. Whatever was the terms of the contract, Ujiyasu actually begun to have a great releationship with the Ninja itself. The two became quite fond with each other, with both constantly teasing each other about their lives. Fuuma followed Ujiyasu until Ujiyasu's death in 1571 peacefully in his bed, where Fuuma retired from the leadership of the clan and passed it to his son who passed to protect Ujiyasu's son and so on. The bond between the Hojo and Fuuma linked the legend between the two leaders forever, even after death.
Normally Ujiyasu would never be summoned on a Holy Grail War, because he lacks the ambition to be part of said battle. Even if he were to be summoned Ujiyasu would prefer to just chill out all day. He doesn't have any particular wish for the grail, he is kinda sad that Odawara eventually fell under his grandson family, but he could see that Japan is in alright place right now, so he can swallow the loss of his clan. So really there is really no reason for Ujiyasu to be summoned for a war. But maybe, under the desperate wish for help and a quiet life, the crafty man descends upon the battlefield once again, to ensure the safety of this peaceful life. And heck, now that Ujiyasu is down here he might as well help his neighbors. There is time.