“Whoever makes the first move wins.”
First Move (先手, Sente) is the twentieth chapter of the Death Note manga series.
At To-Oh University, Ryuzaki challenges Light Yagami to a friendly game of tennis. Light warns his opponent that he is a skilled player, but L tells him that he was a junior tennis champion in Britain.
Light wonders if Ryuzaki is actually British and if asking him will seem suspicious. He asks the question anyway and L answers that he lived in Britain for about five years, but adds that that fact will not help narrow down his real identity.
Light wonders if Ryuzaki is planning to analyze him by observing the way he plays.
Ryuzaki doubts if he will get any good evidence out of a simple game but can’t rule out the fact that Kira hates losing.
Ryuzaki starts with a cheap shot. He and Light exchange pleasantries about striking so early in the game and L taking him by surprise—which is not the first time he has done so.
Yasunaga, the master in charge of the tennis courts, is chatting up some young girls when he is told that the students who got the maximum scores in the entrance exams are playing on the courts. Unauthorized use of sports equipment is forbidden so he decides to go and have a word with them. When he arrives at the court a crowd has built up. Gobsmacked by the players' performances, Yasunaga cannot bring himself to stop the game and wonders if they really are amateurs.
Before long the crowd has doubled and a chair and line umpires have taken positions in order to keep score. Yasunaga is told that Light Yagami was a Japanese junior national tennis champion two years running but then gave it up in order to focus on his studies. On the other hand, nothing can be found out about his opponent who is doing such a great job of standing up to the champ.
On the court, the two competitors go at it with all the energy they have, but their minds are on other matters.
Ryuzaki knows that Kira hates to lose, but then again, he is not the only one who has a will to win.
Light wonders if giving the game his all will give him away as Kira and if it would seem natural to deliberately lose. But then, a game of tennis is too full of uncertainties to be of any use to the investigation, so why throw it?
Ryuzaki has not mentioned the Kira case since their first meeting—he's waiting for the right moment. Light knows that this game, intended to build up a "friendship," is just for appearances' sake.
Ryuzaki and Light both know that Ryuzaki will soon proceed to the next step, which would be to trick Light into giving away information that only Kira would know.
Ryuzaki revealed his identity to Light and invited him to join the investigation: Light is bound to use that against him. Joining the investigation would be a good way to impede it, and it would also reduce the chances of slipping up and revealing information only Kira would know—but it might also give him away.
As they reach the end of their match, they both know that Light will ask to meet with the Task Force members so as to confirm that Hideki Ryuga is indeed the real L, while Light decides that attack is the best form of defense and strikes so hard with the ball that it passes L.
Light is declared the winner. Sweating and out of breath, the two opponents shake hands and compliment each other's performance. Light invites L for a drink and a little talk. Ryuzaki welcomes the chat, but also warns Light that his suspicions have increased and that he believes that Light is Kira, L having made the first move here.
The chapter's title "First Move" refers to the scene in the chapter, describing that the person who makes the first move wins. After Light wins the tennis match, he invites L to drink some tea. Tsugumi Ohba said L then "makes the first move" as he needs to tell Light something before they drink tea.
Originally, when considering what L and Light would compete in, Ohba had considered having them fence or play golf instead of playing tennis. However, fencing requires that they cover their faces, and golf probably wouldn't be something that would draw a crowd, and so tennis was decided on.