As one of the Lords of the Clock Tower as well as the department head of the Modern Magecraft Theories department, Lord El-Melloi II holds yet another lecture for his diverse array of students. After the post-lecture meeting with other Clock Tower nobility, he throws out a few insults at the fellow Lords that are interested only in their internal power struggle, but he quickly receives a counter-curse in retaliation. On the following day, while in transit with his apprentice Gray, he notices a cat ran over by a car. It's the stray cat that frequently visited his room as of late. Lord El-Melloi II realizes that this was an attempt to take his own life, and commences a perpetrator hunt along with Gray, Flat and Svin.

[Source: Crunchyroll]

Waver Velvet – The boy who fought side by side with the King of Conquerors, Iskandar, during the Fourth Holy Grail War in Fate/Zero.

Time has passed, and the mature Waver has now adopted the name of Lord El-Melloi II.

As Lord El-Melloi II, he takes on numerous magical and mystical cases in the Clock Tower, the mages’ mecca...

[Source: AniplexUS]

A letter is delivered to Lord El-Melloi II informing him of a Clock Tower reunion.

One morning, as the reunion's date draws near, Lord El-Melloi II takes a look in the mirror and reels in shock. He is suddenly a full decade younger! Lord El-Melloi II has become Waver Velvet, his former self!

Believing himself to be in the grip of a powerful, magically induced delusion, Lord El-Melloi II immediately begins investigating how this could have happened.

On the day of the reunion, he makes his way to the gathering of his contemporaries, planning to confront whoever transformed his body and hoping to reveal their intentions.

However, when Touko Aozaki arrives, things take a sudden turn...

[Source: Crunchyroll]