 If you liked
Btooom!
|
 ...then you might like
Gleipnir
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Both are set in same natural environment and have fights for survival there.
Gleipnir resembles Btooom! Both series take a battle royal approach and contain content such as violence and sexual themes (not straight/borderline H but more than your average anime). Both are action-packed series with very sadistic and sometimes fragile (regarding trauma or mental state) characters and have verdant sceneries (Btooom!: tropical island, Gleipnir: part of it set in a forest). Sure, Gleipnir has a cast with powers while Btooom! stays somewhat realistic, but because of their similar traits if you enjoyed one and wanted a different set of circumstances that retained that survival aspect, then check the other.