Webnovel series by Tekkou Kaijin. Title roughly translates to I was reincarnated as an anonymous fighter in a Japanese fantasy erotic game, but all the women around me were crazy and I had a bad feeling about it. It's a reincarnation story about a fictional eroge named Yami no Hotaru.
Shorthand it is generally referred to as Yami no Hotaru after the setting eroge. All the love interests are yandere.