Heroes or Champions are mighty warriors who are capable of battling against the (often superhuman) power of monsters. Your average human can be casually defeated by even a low-level monster; "hero" is a catch-all term for those who are strong enough to defeat or fend off most monsters.
Favour of the Gods
Heroes have existed for as long as the Monster Girl Encyclopedia world itself, raised up by the Gods to destroy the Demon Lord since time immemorial. After attacking the current succubus Demon Lord in person didn't end so well for her, the Chief God and her Order have made the training of heroes a central pillar of their strategy to combat the monsterized menace. The usual route to become a hero seems to be a combination of rigorous training and holy blessings. The Theocracy of Lescatie specialised in producing top-ranked heroes, although powerful human warriors can arise from outside the Order as well: e.g. Zipangu's Amanomiya Koyoi .
Although some heroes are made, others are born. Humans chosen by fate (rather than an Order drill sergeant) to become heroes may find their development watched over by a valkyrie sent from Heaven. Conversely, if an echidna monster girl sniffs out a young boy's hero potential first, she may disguise herself as human in order to groom him into the perfect husband.
The Demon Lord's husband was once a hero, before he started fraternizing with the enemy and switched sides. The spirit corruption in Royal Makai is so intense that this is the fate of many, if not most, of heroes sent to destroy the Demon Lord; so much so that there is a whole unit of monsterised former heroes in the Demon Army, notorious for not doing much other than sex all day.
Human warriors appointed by the order whose mission is to slay the Demon Lord. They have been granted strength by the “chief god,” and possess far more fighting abilities than an average human. It is said that up till now, many heroes have set out on the journey with comrades, but almost none have ever safely returned. Perhaps because the majority of them are charmed by monsters and choose the path of living with a monster.
Humans are the most proliferate form of intelligent life that inhabits the world. The magical power and physical abilities of humans who haven't received training are far lower than that of the monsters. Most humans are no match for attacking monsters, and they're easily knocked down, which leads to coupling, and soon after, they're taken home by the monsters.
However, depending on training, the abilities of humans can grow immensely. Those who have received advanced training, those who have gone through many battles, those receiving divine protection, etc. are called “champions” or “heroes.” They are far more powerful than an average monster.