As mentioned in the comment, "Easter Island Epitaph" is the 35th episode in series 2 of GeGeGe no Kitaro (1971) anime. However, the manga the story was based on is not from GeGeGe no Kitaro, but from World Mysteries series, another original manga by Shigeru Mizuki.
The World Mysteries series (世界怪奇シリーズ) contains 8 short manga:
- Yōkai Flower Alraune
- The Woman of Angkor Wat
- Easter Island Epitaph
- The Rainbow Kingdom Agartha
- Neko-Mata's Love
- Invitation from the South
- Persian Twilight
- Amagami Yumuchaac
As for the "Easter Island Epitaph" chapter itself, it has appeared in a few publications:
- Big Comic magazine (1968.06.01)
- Rainbow Country Agartha (虹の国アガルタ) (1971.03)
- Kaiki Shinin Chou (1985.01)
- He no Youna Jinsei (屁のような人生) (2009.12)
- The Complete Shigeru Mizuki Manga Collection vol. 69 (水木しげる漫画大全集(069) 世界怪奇シリーズ(全)/サラリーマン死神(全) 他) (2013.07)
Unfortunately, the whole publications haven't been licensed in English, so there's no way to acquire it legally. However, for the original Japanese version, The Complete Shigeru Mizuki Manga Collection vol. 69 can be purchased on:
- Amazon Japan: Printed Comic / Kindle Edition
- Yodobashi (Japanese): Printed Comic / E-book Version (need Doly app to read)
- Apple Books (Japanese) (digital)
- Book Walker (Japanese) (digital)
- or look for the alternatives listed on Kodansha Comic Plus (Japanese)
Sidenote: the reason why GeGeGe no Kitaro anime used another manga series was that there was not enough material to be adapted at that time. Out of 45 episodes, 23 episodes were adapted from non-Kitaro series.
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