Raiden is a Demigod, son of Zeus, the old god of lightning in the land of Olympus, or rather he's the fifth descendant of that lost son. (by the time the events of Kid Icarus (NES) start all the 'old' gods are dead making way for the 'new' gods like Palutena and the rest.) Now Olympus is a haven for the handful of half gods who still remain after an attack by hades, Raiden is the strongest of the demigods and blames the Goddess of light and also the Goddess of Nature for the loss of his land's population during Medusa's invasion during the events of Kid Icarus Uprising. Now there are only a handful of olympians left, very few of which who can use their godly powers. As a result they were captured by Hades's forces while Raiden was focused on defending the village itself.
Not much is known about Raiden, although Magnus admits that he was a member of his 'band of mercs' for a short time. During that time his home was attacked by the now bodiless Hades and the loss of a close friend named Hercules (yes that hercules) Raiden broke off from Magnus's band of mercs and became the self entitled protector of Olympus. Skilled in the art of swordsmanship and martial artes, Raiden lives up to his name by manipulating lightning itself. When asked if he remembers anything about his 'past life' during the many events of 'Kid Icarus: The Lost Blade' Raiden comments that he fought a 'vampire' and died, asking a 'legendary soldier' to avenge his life on his seemingly last breath.
While the reference goes over the other character's heads, Hades, who's the narrator for this story alludes to some 'other game' that the reader might not know about.
Raiden's personality isn't quite as sassy as the other Kid Icarus characters, when he speaks he is often blunt and to the point. Though he does have a few moments of sarcasm that end up with some rather glorious moments of comedy.
Pit: So Magnus said you travel a lot, got any tourist spots?
Raiden: It's not exactly a 'place' .... um... hot springs?
Pit: Yeah~ Hot spriiings~ I knew we'd have something in common eventually! :3
Magnus: Ha, do you want to tell him or should I tell him?
Raiden: Some secrets are best left untold, besides, even if you -did- explain it, do you think he'd get the context?
Pit: Hot. Springs. ~
Magnus: That's.....a good point...
Palutena: How lewd, oh well, at least he's honest?
Palutena: As goddess of light it's my job to accept any human willing to admit their faults.
Viridi: Ugh! But that samurai basically just admitted to being a peeping tom!
Pit: Peeping tom? what's that?
Everyone: You don't need to know Pit...