Revealing elements about this ONA does have some major spoilers for what its true premise is all about, so I'll try to tread carefully with my thoughts on Starlight Promises. But essentially, it mixes elements of traditional Japanese folklore revolving around Tanabata and augmented reality that serve as the major drive for Shoma and Shiori's reasons for becoming part of the festival. This mix is quite creative with trying to preserve historical accuracy in sticking with the established traditions for Tanabata, while adding in a futuristic twist for how its implemented. There is also a decent amount of fleshing out of Shiori and Shoma's characters, which serve as the major crux for why they are at the festival and helps create convincing character drama out of their situations as the film progresses along, especially in the case of Shoma. Plus for an ONA, Starlight Promises is quite a visual pleaser with gorgeous scenery, good-looking character designs, and fluid movement throughout its run.
Praises aside, Starlight Promises is not without its issue. What is revealed about the purpose of the festival is rather predictable if you know about the origins surrounding the Tanabata festival and the film does enough early on to make things clear about what the festival in the film is all about. In addition, there are some action scenes that seemed unnecessary for their addition to the ONA as they didn't mesh well with Starlight Promises' intended premise and seemed to be added in just to pad out the ONA's runtime.
Issues with predictability and pointless action aside, Starlight Promises is still rather creative in its mix of a well-known Japanese holiday and sci-fi, as well as offering some solid character drama out of Shoma and Shiori's situations. I'd at least recommend checking the ONA out at least once if you are interested in a solid character drama.
