A man and his dog. Nothing else you need to know going in, because the show respects you enough not to oversell what it actually is. Hachikou doesn't manipulate you with a swelling score or force a breakdown, it just watches a loyalty so simple and true that it becomes unbearable. By the end, you're not crying because the story demands it. You're crying because you remember what it feels like when someone just shows up, every single day, no matter what.
Anime Hachikou Monogatari is a drama OVA.