The Secret to Strength

 is the second volume of the OnePunch-Man manga series.

Summary
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Chapter list

 * 9th Punch: House of Evolution
 * 10th Punch: Modern Art
 * 11th Punch: The Key To His Power
 * 12th Punch: Paradise Group
 * 13th Punch: Speed
 * 14th Punch: Don't Know You
 * 15th Punch: Hobby & Work
 * Volume 2 Extra
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Release info

 * Release date: December 4, 2012
 * ISBN: 978-4-08-870702-0
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