Negative Happy Chainsaw Edge (ネガティブハッピー・チェーンソーエッヂ) is a manga series by Tatsuhiko Takimoto. It was serialized in Shonen Ace.
Yousuke Yamamoto is a typical underachiever, searching for a reason to live while struggling to come to terms with the death of his friend Noto a year ago. Everything changes dramatically for him one night when he runs into Eri Yukizaki, a beautiful girl hiding a tragic loss of her own, out on the streets. When a chainsaw-wielding giant falls from the sky and engages her in battle, it marks the beginning of Yousuke finally finding his purpose in life.