This is a battle between healthy food sellers. The plaintiff registered a trademark for "CaricaCelapi," which is a healthy product made from papaya. The defendant bought the keyword "CaricaCelapi" from Yahoo Japan and whenever a user inputs "CaricaCelapi" to search, the defendant's advertisement is shown, indicating that the defendant sells healthy food made of papaya. The plaintiff sued the defendant for trademark infringement. The court denied, finding that defendant's advertisement does not constitute a "usage" of the plaintiff's trademark.
There are three important points. First, Japanese Trademark Law lists eight categories of "usage." Article 2(3). The most relevant is putting the trademark on an advertisement. Article 2(3)(viii). The court seems to believe that as the trademark itself is not included in the defendant's advertisement, the plaintiff's trademark is not "on" the defendant's advertisement and therefore there is no infringement.
Second, the plaintiff is apparently not good at arguing this line of argument. The court mentioned that there is no explanation from the plaintiff why the keyword purchase is "usage."
Third, the court ruled nothing about the cases where the keyword is actually displayed within the advertisement. For example, if Uncle Sam advertises "Pay Less for Aunt Terry's Apple Pies!" that might constitute an infringement.
As this is just a lower court case, it is difficult to assess how persuasive this opinion is. However, if a trademark owner wants to win, she should persuade the court that the purchase of her trademark as a keyword somehow constitutes "usage."