Heroism is related to Fighting in Japanese, it's not the Heroic type. Fighting/Dark for a Batman Pokemon.
Tell me how much Japanese you know and give me a reliable source. Without source anything said has no much credibility.
Batman could be considered "dark-type" for the following reasons:
-He uses darkness as an advantage -He fights only in the night, where there is darkness -In some incarnstions, Batman was thought as a villain, but later he was proven to not be one -His Batcave is a dark place surrounded by darkness, full of bats -Darkness is considered to be evil, Batman has a "evil" suit to cause fear, a negative emotion, to his opponents. -Batman is not evil, but he takes the appereance of one to strike fear into his opponent. -His suit is black, has a dark appereance.
In conclusion, Batman is a good guy, a hero, but he uses things in contrast of the likes of King Supez that use light. If you are going to look for excuses to prove me wrong GTFO GameFAQS and call DC Comics and argue with the creators of Batman why he is not a dark knight and watch how they prove you wrong.
Across the highest mountains, into the endless seas, our journey ever onwards fight until we all be free