This is Sana's Mama, a popular novelist who won an Aoki award for her writing. She's a very cool lady with a squirrel living on her head. That's not the only peculiar thing about her head, she also wears many eccentric shaped hats -  houses, the eiffel tower, playgrounds, a tree, a water fountain, she's done it all. Mama may seem really weird, and carefree, but in fact she's... well actually she's...you know she's...just really weird and carefree. ^__^
Rei-kun! Heheh... This is Sana's manager, and pimp! He may seem to be one of the sanest in the Kurata household, but Rei has his quirks, and many secrets about his life were delved in the beginning of the series. As a manager, Rei is determined to make Sana the most well done in Japan. He's quite demanding and clueless really, once making Sana do 7 commericials in one day. Despite all that, Rei loves Sana very much for giving him a chance in life... *spoiler edited* ;P
Tsuyoshi desu. He's Hayama's best friend since kindergarden. Stereotypically, Tsuyoshi-kun is your nerd, the shy, timid guy who gets the best grades in class. That would be the complete case if the show wasn't Kodocha. ^_^ While usually calm and rational, Tsuyoshi occasionally have 'breakdowns' (especially when ppl make fun of his mama) where he goes BERSERK. Hayama has to karate chop him to shut him up. One of the many reasons for their friendship. 
Zenjirou is the teacher from the show ever popular show 'Zenjirou's Kodomo No Omocha'. Zenjirou sensei is awesome! He's wacky, pathetic, corky, spastic, funny, and definitely one of the main contributors to the antics of the show. Zenjirou gets upset at Kodocha often because the show keeps making fun of him (he gets picked on, nobody knows who he is, etc. heehee). Sana and Zenjirou have a tight relationship. They are both weird people and hit off well. 
It's a bat! It's a rabbit! It's a..... BABBIT!!! ^^;; Babbit is the mysterious strange creature that comments on the show. He/she tells you important background information, silly translations, but most of the time, he/she makes dumb comments. He/she enjoys making fun of him/herself and the people on the show who loves to ignore him/her. ^_^ But Babbit can be funny, just everyone else. And yes, I am clueless of his/her gender.
Aya is one of Sana's good friend from school. Shy and timid, it may be unexpected that she has a boyfriend. It's more unexpected that her boyfriend is... Tsuyoshi!!! Hahaha. I guess similiar can attract after all. Yeah yeah, they like each other... puppy love, uh-huh. They are kind of cute, the couple I mean. In a timid, whispery voice way. Or maybe I'm just saying that to fill space. Hmmmm...hmmm...hmmm... lalala...
Lookie, it's Hayama-chichi. Hayama's dad is calm, gentle, and monotoned, however, he is clueless outside of work. Chichi isn't the world's best dad and often ignores Hayama until *spoiler edited* ;P. When he does act more caring, Hayama-chichi is a pretty cool, he spoils Hayama with sushi.  :) Like the other characters, he's also weird. Occasionally, you'd see him do something arbitrary, breaking his stoic facade. Hehee.
*Stares at picture at left* ROFLMAO. :D NaruNauru is Sana's elementary school principal. His egg shaped um... head makes him one of the most unique looking people of the show. In addition, he is indeed, one of the more unique people in Kodocha. NaruNaru is friendly, good going, everyone's favorite principal because he's so darn lenient and happy happy genky genky dumb dumb. He's also the one that encouraged Hayama to take up karate, so props to him!!