The first short story focuses on Favaro and Kaiser between the events of the first and second series as they visit Favaro's home village. The second short story shows Kaiser as a knight commander sparring with Jeanne, and sharing the reasons they remained as Orleans Knights in the aftermath of the final battle against Bahamut.
9Anime is the best site to watch Shingeki no Bahamut: Genesis - Short Story
SUB online, or you can even watch Shingeki no Bahamut: Genesis - Short Story
DUB in HD quality. You can also find MAPPA
anime on 9Anime website.