Definitely my go-to-list if anyone asked about the first anime to make me cry. While yes the MC is the most crybaby MC I have ever encountered, it's kinda justifiable if you read the manga. The OPs and EDs are definitely superb and compliment the story. Tegami Bachi world setting is definitely one of the most out-of-the-box I've seen. A Sunless world, where the Sun is a mere fairytale. A world of cat-eyed humans who seek to get closer to the artificial Sun. A world where memories and emotion matter the most. Also big insect monsters?! I'm sold. While it looks like a simple or childish story,its depth is good and shows us how precious the work of Letter Bee.