I found Blog with very cool material, some SF2 designs and game mechanics book, its not in english but its great to see how its done professionally 
http://videogamesdensetsu.tumblr.com/page/4
Here are some wakuwaku sequel designs which probably werent even translated to pixels but its cool to see them and all new characters, this game is for me better with age because now i see how fantastic designs were for its time and its too bad we didnt get sequel made.
http://videogamesdensetsu.tumblr.com/post/167621952240/shin-waku-waku-7-%E6%96%B0%E3%82%8F%E3%81%8F%E3%82%8F%E3%81%8F%EF%BC%97working-title-part-1
http://videogamesdensetsu.tumblr.com/page/4
Here are some wakuwaku sequel designs which probably werent even translated to pixels but its cool to see them and all new characters, this game is for me better with age because now i see how fantastic designs were for its time and its too bad we didnt get sequel made.
http://videogamesdensetsu.tumblr.com/post/167621952240/shin-waku-waku-7-%E6%96%B0%E3%82%8F%E3%81%8F%E3%82%8F%E3%81%8F%EF%BC%97working-title-part-1