It's quite a mystery right now, but sometimes I swear that every character in this manga secretly wants to get in his pants (and Ultimo's too.)
And with these looks it's no freaking wonder:
Yamato Agari is originally presented in the manga as an idealist 12th century bandit swordsman who reunited an army of his own to defeat the oppressing Japanese nobility once and for all, and start a new government ruled by the people themselves.
Interestingly enough, not really much is known about him except for the fact that he reincarnated in todays 21st century as a 16-year old high school student (as well as his comrades), until he finds a certain doll in an antique shop and he feels a strange connection with him.
Ultimo (a super robot representing Ultimate 'Good') awakens to the presence of its master and embraces him, despite him not having a clue as for why.
Yamato is the master of this douji who has the ability to control time and dimensions, and it's the most powerful of its kind. Precisely because of that absolute power is that everyone wants to get a hold of it, and it's believed that it's actually the cause for the future destruction of the world as we know it, because of the expected ultimate clash with the douji (robot) of absolute evil, Vice.
Yamato's challenge is to figure out a way to stop this cataclysmic event from happening and capture Dunstan, a scientific genius criminal (sought after by the Guardians of time), who created all these robots of Good and Evil just for his amusement.
And at the same time, Yamato finds himself just wanting a normal life with his high school sweetheart, Makoto Sayama.
It's good to note that Yamato is drawn as a 'man among men', and much taller than his classmates, he has this classic 'Samurai hero' look and always displays a noble attitude, despite being bad-tempered.