The Holy Grail of Eris (エリスの聖杯, Erisu no Seihai) is a Japanese light novel series written by Kujira Tokiwa and illustrated by Yuunagi.

It began serialization online in October 2017 on the user-generated novel publishing website Shōsetsuka ni Narō.

Written by Kujira Tokiwa, The Holy Grail of Eris began serialization online on the user-generated novel publishing website Shōsetsuka ni Narō on October 16, 2017.

[3] It was later acquired by SB Creative who published four volumes with illustrations by Yuunagi under their GA Novel imprint from November 14, 2019 to March 12, 2022.

A sequel manga illustrated by S.Kosugi, titled Eris no Seihai S, published its "0th" chapter on Drecom Media's DRE Comics website on October 18, 2024.