#!ruby -p
12.times{|i|sub /#{%w(iwa$ tou$ wa$ u(nara) k[^\ ]*e$ you$ ^ita.*a ^itt.* ima$ ma$ ^m[^\ ]*o ^su[^\ ]*)[i]}/,%w(\&n \&sagi \&ni \1ion nakamaga\ popopopo-n \&nagi \&u \&kanku \&nbou \&usu tanoshii yukaina)[i]}
Note that non-ascii characters in the above source code will be escaped (such as \x9f).