Read manga: Shishunki No Iron Maiden

manga
Summary:

Mayama Haruki and Himemiya Tsukiko have been childhood friends and neighbors for as long as they can remember, but after a girls-only meeting in fourth grade, Himemiya distanced herself from Mayama. Now in their 2nd year of middle school, Mayama has become an ero-freak who specializes in harassing Himemiya.Determined to unravel the greatest secret of girls, what happens on "that day", Mayama follows Himemiya and uncovers...!("that day" for girls may not be what you think it is)-from mangaupdates-

Chapters (41)
Aug 25, 2019
Chapter 1 : 'that Day' Of Hers
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Chapter 2 : Tsukiko's Secret
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Chapter 3 : Not Eating What Is Set Before You
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Chapter 4 : Iron Will
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Chapter 5 : That... Has Come Out
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Chapter 6 : A Close Call
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Chapter 7 : I'm Nonoa
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Chapter 8 : That Girl's Observation
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Chapter 9 : Iron Protrusions!
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Chapter 10 : Secret X Secret
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Chapter 11 : A Play Back Of That Day
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Chapter 12 : Looking For The Culprit
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Chapter 13 : Howling Boy!
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Chapter 14 : Coming Out!
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Chapter 15 : Thin Ice
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Chapter 16 : Another Observation...
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Chapter 17 : Ptm: Peeping Teacher Minowa
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Chapter 18 : It's Show Time!!
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Chapter 19 : History's Biggest Battle Plan
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Chapter 20 : Nonoa's Gloomy Day
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Chapter 21 : The Passing Days
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Chapter 22 : Coward
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Chapter 23 : The Confession
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Chapter 24 : Run Young Man!!
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Chapter 25 : If The Tears Poured
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Chapter 26 : Charm Maiden
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Chapter 27 : The Second Album
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Chapter 28 : From Pure White To Purity!
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Chapter 29 : First Confession
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Chapter 30 : Bye Bye Xxx
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Chapter 31 : Fuck You!!
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Chapter 32 : Read Online
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Chapter 33 : Uneasy Days
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Chapter 34 : The Princess, Captured...!?
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Chapter 35 : Read Online
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Chapter 36 : Observing The Observation Diary
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Chapter 37 : The Truth Behind The Metamorphosis
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Chapter 38 : Remember!
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Chapter 39 : The Great Escape
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Chapter 40 : Secret Base
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Chapter 41