Inspired by the Global Conquest Mode in Command & Conquer 3: Kane's Wrath, the basic concept of "EvaWars" would be a 4X game that incorporates "character-focused" tactical combat - something akin to MechCommander or XCOM: Enemy Unknown. A modified version of the Neon Genesis Evangelion setting seemed the most appropriate model to explain or illustrate the concept.
The strategic level issues are largely similar to the Civilization games, Sid Meier's Alpha Centauri, etc. in that the players build cities/bases in order to develop their economy, conduct research, and produce military units. As in those games, players can mobilize troops, vehicles, and aircraft to attack enemy forces or defend against enemy attacks.
The twist comes from the inclusion of Evangelions (or Evangelion-esque mechs), which are almost completely invulnerable to conventional attacks but are limited by the requirement for a compatible pilot. When deploying Evas against enemy forces or facing enemy Evangelions, players take control of their forces in a tactical battle mission (as in Kane Wrath's Global Conquest). Although the only thing that can successfully engage an Eva in direct combat is another Eva, conventional forces can disable enemy Evas the (mobile) reactors/microwave transmitters supplying it with power. In an Eva vs. Eva battle, destroying the reactors/transmitters isn't as useful because Evas can use enemy transmitters.
As with MechCommander, individual Evas can be customized with different equipment. Similarly, unlike the Evangelion show, pilots are not matched to specific Evas, so a pilot can be swapped into a better unit when new research makes the production of better Evas possible or when an operation calls for the use of a different Eva.
Given that the game would involve multiple types/classes of Eva, one possible mechanic would be for pilot's abilities to synergize differently with each type of Eva. For example, if a pilot has a "Berserker" ability, that might give the pilot a bonus in "hand-to-hand" when using a Grappler-type Eva, but increase hit change and ammo usage (due to better spray and pray) when using a Gunner-type Eva.
