It's not uncommon to see other developers borrow certain ideas from previously release games to use in theirs, like weapon swapping and other features along those lines. However, Capcom believes that Koei Tecmo went a bit too far with a feature it's been using in its Dynasty Warriors game.
Capcom recently filed a lawsuit against Koei Tecmo for patent infringement, according to a report from Sankei. The basis of the suit revolves around a patent Capcom filed twelve years ago (in 2002) that allows gamers to acquire new content by combining an existing game with another piece of software. It turns out that Koei Tecmo has been using a similar feature with various Dynasty Warriors titles, starting with the release of Samurai Warriors: Xtreme Legends, allowing players to perform a similar technique to unlock content.
Controller vibration to notify when an enemy was close was also mentioned in the suit, a feature Capcom believes "has greatly contributed to the sales" of Koei Tecmo's Warriors series.
With the suit, Capcom is seeking a five to ten perfect ratio of the series' overall sales, which clocks in at around 9.73 billion yen. They also expect some of the titles to be discontinued in sales, although specific games weren't mentioned. Koei Tecmo has not yet responded to the suit.