Some of the ovas are omakes created by Mashima (extra manga chapters) or chapters from the original manga that were not adapted into the anime. Fairy Tail S is a manga which compiles the omakes created by Mashima. Although some omakes are also adapted in the anime, maybe you remember the episode where Natsu brings a colored tree to Lucy at her house? It is an extra chapter that Mashima created and it is compiled in Fairy Tail S. There are also extra chapters that come with the compilation volumes of the original manga, some of those were not adapted to the anime and others were, an example of these are episode 49 and 50 of the anime based on the predestined meeting of Lucy (Natsu) and The first time when Lucy thinks of Natsu as a romantic couple. It's been a few months since you watches the episodes, but to they are some examples.
The OVA are crazy , the funny thing is the more you continue with them the more fan service became crazy and i'm not kidding , my favourites OVA are 5 - 7 and 9
This month they release the figure of Lucy wearing the cat suit from ova 1 again but a Halloween version and as the Lucy fan that I am I must have it. thanks for the ovas ❤
