Japanese online shop Rakuten has a pre-order page for Rockman EXE: Operate Shooting Star that shows what Capcom has been trying to hide so far: the battle system. One sole screen shows a battle window that looks virtually identical to the one from the original MegaMan Battle Network. The only noticeable difference is that the custom window only has two lines instead of three, which show the letter code for each chip - basically how the chip system worked from Battle Network 2 and on. This makes me also wonder if OSS will have * chip codes. Additionally, they've also announced a minigame included in OSS called the Rockman Star Colosseum, or "RockColo." While lacking in details, it mentions the game consists of versus battling, and up to six players can play wirelessly with just one cartridge, which sounds similar to Star Force 2's Sky High Colosseum.
With this leak of the battle picture, I expect a full reveal of the battle system from Capcom pretty soon.