"Bokosuka Wars" (1983), a game regarded as the progenitor of the strategy/simulation RPG genre, is also difficult to clearly define. While often referred to as a strategy/simulation RPG, it is also sometimes referred to as a prototype real-time strategy, an early reverse tower defense game, and an early action role-playing game. "Nobunaga's Ambition" (1983) and later Koei titles as well as Capcom's "Destiny of an Emperor" (1989) have blurred the line between a role-playing game, turn-based grand strategy wargame, and simulation video game. Similarly, Kure Software Koubou's "Silver Ghost" (1988) combined elements of both tactical RPGs and action RPGs, while "" (1993) blurred the line between a tactical RPG and a real-time strategy. "Metal Gear Acid" (2004) blurs the line between a stealth game, a genre the "Metal Gear" series is normally known for, along with tactical role-playing inspired by the likes of "Fire Emblem" and "Final Fantasy Tactics", infused with card gameplay found in games like Konami's own "Yu-Gi-Oh!" series.