Daigo is an Azurite noble and former infantryman.
He and Kazumi Kato fought alongside the Order of the Stick during the battle of Azure City and met her when they become trapped in a tower with the Order, at which time she asks him out on a date should they both survive the battle.
While they were originally unnamed and undifferentiated members of the Azure City army, they reveal their names to each other in order to dodge the fate of all nameless redshirts (that is, to be killed horribly while the main characters survive), although Daigo refused to reveal his last name as he is "saving it for an emergency". They then escape the city aboard Lord Hinjo's junk.
During their time in exile, Kazumi and Daigo fall in love and conceive a child, leading them to ask Durkon to officiate at their wedding. Hinjo rewards their service with a noble title, forming House Kato after Kazumi, since Daigo's surname is still unknown.
Daimyo Kubota, marked them for assassination as part of his plan to seize control of Azure City, hoping to remove their votes from the council of nobles who would choose the leader following Hinjo's death.
Daigo was later seen on the Orc Island along with Elan, Durkon and Lien hunted by Orcs. When Elan presented Banjo to them, the Orcs started to worship him and attempted to kill the visitors because they were not worthy to keep him. Lien did not manage to leave and was left behind to be sacrificed to Banjo; eventually the 3 men returned to rescue her.
Chief Grukgruk intended to kill them all, but Therkla impersonated Banjo and demanded to let them free. Qarr then hypnotized Grukgruk only to be dispelled by Durkon. Therkla lead them through a Greg Initiative tunnel before Vurkle realized the prisoners had left with Banjo and the tribe ran after them.
In strip #586, "No Encounter is an Island Unto Itself", Daigo spectulated that he and Kazumi's unborn child may be a Monk based on the amount of kicking it was doing.
In Entrance Qualifications, Daigo reveals the first two letters of his last name (Da) before being interrupted by Therkla.