This is an Anime in which you can hear both the daily conversation between high school students and between the adult characters. It basically consists of plain terms and simple conversations, so I can recommend this to Elementary-level Japanese learners.
Compared to other anime, there are very few characters introduced. And the conversation between Chito and Yuri is the main plot point. Because they both speak at a slow speed, it is very easy to understand. A few technical military terms appear, but since most of the conversation consists of plain terms, I would like to recommend it to elementary level Japanese learners.
In this Anime we can learn Japanese in both somewhat reserved manners and friendly manners, as the main character is a secondary school student who returned to Lake Kiriya City after seven years. Note also the word in the title which you write “天体” (てんたい, celestial) and pronounce “そら” in this Anime.