Volume 20 splits between the pre-storyarc leadup that started in Volume 19 and the actual beginning of the new Magic World arc. Like before, the leadup is light in nature as it feels like Akamatsu is making up for the loooong Mahorafest arc with these mini slices-of-life of various characters (probably because you won't be seeing most of then until the Magic World arc is finished).

The highlight of this portion of the volume is the reintroduction of Negi's childhood friend, Anya (who you see in the cover). With her fiery personality and jealousy, mixed in with a group of over endowed Negi fans, and you have a recipe for disaster (or hilarity).
The latter third of the volume is devoted to the beginning of the Magic World story arc and the action goes quickly into overdrive.

A fun volume as usual, though you should start from the beginning of the series to know who's who and what's what. ( )