Toki wo Kakeru Shoujo, Ano Natsu de Matteru Recommendations
Apart from the fact that both anime (ovie the one series the other) have the romantic feature as their main feature they have a very similar way on showing how protagonists deal with situations unknown to them!!!
They also have the fact of the unknown for different reason each!
I shouldn't say more because it would be a spoiler but in my opinion these both have more similarities than meets the eye!