Takahashi

Takahashi is a scientist and former colleague of Professor Nikaido.

Plot
When Maki Nikaido is infected by the virus, L takes her to see Takahashi, whose name he remembers as a co-writer of a book with Professor Nikaido. Takahashi scolds L for bringing Maki to him in her deteriorating condition, saying that he had put countless lives at risk by doing so. L asks Takahashi to help create an antidote for the virus, which, at first, Takahashi is dead set against, explaining that he had made a vaccination once before that had ended up killing people. L points out that Professor Nikaido had been successful, and so Takahashi relents, agreeing to help find an antidote.

Trivia

 * Takahashi ultimately plays the same role as Koichi Matsudo in the film adaptation.
 * A character named Takahashi appears in the Death Note: Light Up the NEW World novel, but it is unclear if it is the same person as the character featured in the L: Change the WorLd novel.