Nephilim

Nephilim (ネフィリム, Nefirimu) is a shōjo manga series by Anna Hanamaki. It was serialized in Nemurenu Yoru no Kimyō na Hanashi from 2004 to 2005, with the individual chapters published in two tankōbon volumes by Asahi Sonorama.

Plot
The series follows a bounty hunter called Guy who meets Abel, from the tribe of the Nephilim who live as males during the day as females at night. After Guy learns Abel's secret, Abel is supposed to kill him by tribal law, but instead ends up falling in love.