The main lead getting truth bombs dropped in the middle of the big climatic fight

"The term "truth bomb" can be used to describe a fact that is meant to be shocking or devastating to the listener."

(Spoilers)

In Across the Spiderverse, in the middle of the climax, Miguel reveals to Miles that Peter would have lived if he hadn't been bitten, and that now there's a whole world out there without Spider-Man.

In Zatch Bell, while fighting his brother, Zatch learns that the one to start the fight between the 100 mammodos, and the current king of their world, was his own father.

In Psychonauts, while fighting against his and the coach's traumas, Raz learns that his own father has psychic powers, who proceeds to then help his son find the strength to overcome the traumas.

In Yu-Gi-Oh! Gx, in the final duel of season 3 against Yubel, Jaden learns that they both had a deeper connection that goes down all the way to their past lives.