Mazinger Z vs Kekkou Kamen

One of the first Super Robot manga and the one that introduced most of the traits of the Mecha genre. Constructed with the Super-Alloy Z, Mazinger was built by Professor Juzo Kabuto as a weapon against the Mechanical Beasts of the evil Dr. Hell. Koji Kabuto, the grandson of Professor Kabuto, becomes the pilot of Mazinger Z when his grandfather is killed, and battles from there on against Dr. Hell and his allies. This is the first series that introduced the concept of a pilot inside a Mecha, which all series from then on have followed.

Kekko Kamen is about the misadventures of a student named Mayumi Takahashi who attends a boarding school called Toenail of Satan's Spartan Institute of Higher Education that is run by sexual predators. The teachers are constantly looking for ways to torture or humiliate the students, and from this the teachers derive sexual satisfaction. Takahashi's only protection is from a mysterious figure known as Kekko Kamen.

Kekko Kamen herself is a mysterious figure who hides the face but not the body! She fights evil with nudity, and nunchucks.

(Source: Wikipedia)

After being warped from their universe to that of Mazinger, the Transformers join the fight between Mazinger Z and Dr. Hell's army of mechanical beasts.

A crossover between Mazinger Z and the Transformers series, with each chapter drawn by a different artist.