This OVA is set on Keima's summer vacation although by some unexpected circumstance their old neighbours have visited Together with an old acquaintance from when he was a child. Due to Unfortunate events His summer vacation may not follow his desire for game time.
What's more interesting are the characters who're suddenly introduced that may play a role in megami-hen. There are also lots of events that may pique interest. The new girl is also cute, mysterious, and fascinating. She plays her role well and she fits with the current setting as well.
Conclusion, This OVA is both worth a watch and can be a must watch since it may have a connection to the sequel megami-hen.