THUNDER GOD NEGI!!! Even the chapter's name kicks ass!
Rakan gets owned by a Negi armationed with the Thousand Lightning (funny fact how the stadium commentor calls it a misterious transformation ability) and we get to see Koutaro's beast form once again since that battle in the sealed staircase. Of course there's a 99/100 chance that the battle is not over yet.
PD: contrary to most people, I really look forward to see just how did Ako realize Nagi was Negi, if it was because of that guy who saw Negi transforming of in some other way.