This is a long running shounen manga with some ecchi elements and light hints at nudity. A spinoff manga, called Kenja no Mago SS, fully went to nude fanservice, but sadly only lasted 3 volumes.
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*(download link includes a compilation Kenja no Mago, Kenja no Mago SS, and Kenja no Mago – Extra Story)
Kenja no Mago SS (3 volumes complete)
