The tournaments are presented in a meta context as if they were beauty pageants with Yotsuba, /co/nrad, /co/lette, Hope Corgi, J/aco/lyn, and Jenny XJ9 (Ms)/Johnny Bravo (Mr) presiding as judges.
Yotsuba Koiwai is the main character in Yotsuba&! As the title character of the series and almost every chapter, Yotsuba is usually the focus of each chapter; most stories revolve around her meeting, and often childishly misunderstanding, a new concept or activity indicated in the chapter title. She is noted for her childish energy, unusual naiveté, and iconic appearance.
J/aco/lyn's is a cowgirl depicted wearing a cowboy hat, red vest, blue chaps, cow pattern slip, and black eye mask. "/aco/" is engraved on her belt. Notable for being the first image board created during Hiro's ownership of 4chan.
Back in 2007, /co/ decided to make a character that encompassed all of the board's popular fetishes at the time. Once she was drawn, she was received well enough to remain mostly as is even after the source fetishes that contributed to her design fell from popularity.
If you want pics of /co/lette, there's a HUGE gallery of them on the 4chanhouse shimmie.
/co/nrad's pet, came into existence sometime during or before 2009; has gained notable popularity outside of /co/ as of 2012. He has the powers of a Blue Lantern.
Jenny XJ9, also known as Jenny Wakeman, is character from the 2003 Nickelodeon show My Life as a Teenage Robot. Jenny's personality is that of an eager, young, tomboyish teenager. Jenny is notable for being the first Ms. /co/ champion, earning the title of 'The OG Queen'.
Johnny Bravo is a character from the 1997 Cartoon Network show of the same name. Johnny is notable for being the first Mr. /co/lympus champion and being one of the most dominant contestants in tournament history.