Sorry for commenting on a really old post but Id say Okuu. Both her and Bowser are powerful, shoot/breathe fire, not bright logical thinking wise but have good weaponry. Suika and Yuugi dont have much connection aside from horn(s) and being physically strong.
Also the Bowser-Okuu connection works great with Bowsers Inside Story. Fawful = Kanako, "Lucky Shroom" = Yatagarasu etc...