Total Recommendations: 2
If you liked
Death Note
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...then you might like
Code Geass: Hangyaku no Lelouch
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Lots of strategizing and thought processing. Differences: Code Geass has mechs and is near-future-ish, Death note's MC is a normal guy.
If you liked
Sword Art Online
|
...then you might like
Btooom!
|
Both have a survival theme, both in a survival game setting, both have romance, both have "die in game, die for real" aspect except Btooom! is set irl.