Disclaimer: None of them are mine. I just made this filk up...

Rurouni-man
To be sung to the tune of Particle Man, by They Might be Giants

Rurouni-man, Rurouni-man, doing the things a Rurouni can
Who’s he like, it’s not important, Rurouni man...
Will he be the slave, or will he save the day?
When he's in a fight does he really win,
Or does the villain get him instead?
Nobody knows, Rurouni-man..

Miburo-man, Miburo-man,
Miburo-man hates Rurouni-man
They have a fight, Miburo wins,
Miburo man...

Shisho-man, Shisho-man,
Ego-as-big-as-the-universe-man
Usually kind to the women
Shisho-man
He has to beat up giant man, as only he can, to save the day again
And when he does it’s a happy land
Powerful man, Shisho-man

Chicken-man, Chicken-man, hit by the back of Jo-chan’s hand
Lives his life in gangster land
Chicken-man
He’s got a debt, how can he pay his rent?
Will he ever pay Tae back?
Who came up with Chicken-man?
Gangster-man, Chicken-man...

Miburo-man, Miburo-man,
Miburo-man hates Chicken-man
They have a fight, Miburo wins,
Miburo man...

Miburo - What they call Saitoh, basically short for Mibu no ookami, i think

Shisho- 'Master', what Kenshin calls Hiko

Chicken-man - Refers to the nickname for Sano

Rurouni-man - Kenshin!!!