In what episode does Gon fight Pitou/Neferpitou (Gon vs Pitou)? 

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Gon fights Pitou(Neferpitou) in the Anime Hunter X Hunter 2011 Episode 131 with the title: “Anger x and x Light”. 

 

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Episode Summary:

Pitou informs Gon that there is no way of saving Kite since he is already dead. Devastated by that news, Gon goes into rage and summons the power needed to defeat Pitou (Pitou notes that his power was equal to the Ant King) which would come at great cost to him.  After transforming, Gon leads Pitou outside Peijin where they began their fight. Neferpitou using Terpsichora on herself proved to be no match for Gon as she was incapacitated by a very powerful combination of attacks.  Killua arrives on the scene a moment before Gon Smashes away Pitou’s head. The battle ends with Pitou dead and Gon losing one of his arms.

 

Kite's Body

Gon Transformed

Gon Transformed

Pitou attacks Gon Killua arrives at the battle