re = /(^<\d{4}> )|(\\(\w+)?\{.*?\})/m
str = '// Resources for SEEN0001.TXT
#character \'美佐枝\'
#character \'春原\'
#character \'ボタン\'
<0000> \\{美佐枝}You little goblin...
<0001> Unable to contain her fury, Misae grabs both of Sunohara\'s legs...
<0002> \\{春原}Heh?
<0003> ...and proceeds to use her killing move, The Giant Swing.
<0004> \\{美佐枝}Uryaaaaaaaaaaaaaaaaaaa!
<0005> \\{春原}Uwaaaaaaaaaaaaaah!
<0006> \\{ボタン}Puhiiii.
<0007> \\{春原}Uwaaaaaaaaaaah!
<0008> \\{春原}Uwaaaaaaaaaaah!
<0009> \\{春原}Uwaaaaaaaaaaah!
<0010> \\{春原}Geeh!
<0171> \\size{intA[1001]}*BOOM*\\size{}\\shake{4}
<0145> \\size{intA[1001]}Dammit! Stupid rugby players!!\\size{}
'
subst = ''
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html