Nobunaga's Ambition

Nobunaga's Ambition is a strategy game made by Koei, the first installment being released in 1983. The game puts you in the role of a daimyō in Sengoku-era Japan, your goal being to unify the country and earn (or with one clan, keep) the title of Shōgun. As long as this series remains largely unchronicled in the West, the article on Wikipedia has a brief history of the series you might find relevant. 13 main-series games have been released in Japan, scattered across an army of platforms.

As of December 17, 2011, a crossover game titled Pokémon Conquest, featuring elements from Nobunaga's Ambition and Pokémon, has been confirmed. It was released by Nintendo and Tecmo Koei on March 17th, 2012 in Japan. Fans went wild, especially from the Pokémon side of things possibly due to the Darker and Edgier crossover aspects.

This game series provides examples of:
 * Badass: Some of the generals qualify easily. Azai Nagamasa and Sanada Yukimura can easily shoot up the ranks when in cavalry units.
 * Crossover: Pokémon Conquest. Standard Not Making This Up Disclaimer applies.
 * Gender Flip: The latest title in the series has a female version of Uesugi Kenshin.
 * Probably a Shout Out to Sengoku Rance's version of Kenshin.
 * Multi Platform: This series has hit most of the popular consoles since the NES, a few that weren't, a bunch of (rarely mutually compatible) 1980s Japanese PC brands, and most iterations of Windows since the 1990s. Also a couple of ports for Macintosh, and one for Amiga.
 * Nintendo Hard: In the NES version, it's possible on higher difficulties to die before your first turn.
 * No Export for You: Of 13 games, only five have been released in the United States. There was a 14-year window with no North American releases between the SNES game Lord of Darkness and the PS2 Rise to Power.
 * Which are still five more than Europe got.
 * Rule of Cool: What other Pokémon to give Nobunaga himself (in the Crossover) than the Badass Ensemble Darkhorse legendary thunder dragon Zekrom?
 * Spin-Off: The Dynasty Warriors-based Samurai Warriors. It may have been instrumental in getting a U.S. release for Rise to Power and Iron Triangle.
 * Video Game Cruelty Potential: Just as in Romance of the Three Kingdoms, you can execute captured generals (or even your own retainers) on a whim.
 * Video Game Long Runners: Thirteen main releases since 1983, not counting all the little differences between ports. Not so many as its sister series, but still respectable.