 If you liked
Kanojo wo Mamoru 51 no Houhou
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 ...then you might like
Let's☆Lagoon
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The front part of Let's Lagoon! is pretty similar to Kanojo wo.... as both main characters knew each other, only not well, before a disaster takes place with the main male character mostly helping the girl.
Diff is that Let's Lagoon has a lot of mystery and involves island survival while Kanojo wo.... is more drama-based and involves disaster survival.