 If you liked
Tadashii Kodomo no Tsukurikata!
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 ...then you might like
Wagatsuma-san wa Ore no Yome
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Wagatsuma-san's main character has to ensure that he marries his high school crush because they're married in the future, however the manga is harem so you know what that entails.
Tadashii Kodomo's main character has to ensure that he marries his childhood friend because the future of humanity is at stake.
Which means that the manga both include time travel and efforts to win over the main character's crush. Tadashii Kodomo has less comedy and more harem, Wagatsuma-san has funny gags, references, 4th-wall, but no action.