Leo Demonheart

Leo Demonheart is the former hero who was denounced by the human world after saving them from the Demon Army because of his unparalleled power. In Tokyo 2060, he was created by humans to fight back the demons. He is the strongest of all of the Twelve Demonheart Series. He is the titular male protagonist of the Yuusha, Yamemasu series.

Appearance
Leo has the appearance of a young handsome man with short black hair and striking red eyes. He wears a greyish-white long shirt along with a short black tunic hoodie which is usually put off, a pair of light brown fingerless gloves, a brown belt along a brown suspender hanging on the left side around his waist, black pants, and a pair of black high boots.

During his hero days, he used to wear heavy armor with a long navy blue cloak.

During his Pre Creation Era he had longer hair and a somewhat androgynous appearance. He is also said to not have a gender, but was created to appear masculine.

Pre-Creation
Initially being created as a bioweapon by Humans to battle against Demons coming into the Human world by a hole, Leo had no emotions or feelings other than killing the demons and protecting humankind. He used to have a composed demeanor, carrying an expressionless face most of the time, and keeping a cool head in decision making and planning.

After meeting a certain demon, he changes drastically, and the demon becomes his first friend. The demon teaches him about human feelings and how he should stop following others orders and instead should live for himself.

Post-Creation
As the sole survivor of the Twelve Demonheart series and unable to grow old, he stuck to the mission of saving mankind that was incorporated into him as a bioweapon for 3000 years.

Throughout his life, he defeated many Demon Kings, thus being famously proclaimed as a Hero and acknowledged as "The Strongest Being" by mankind. Over time, though, Leo gradually changed as he came to the conclusion that he has an insatiable hunger for being a Hero and fears lasting peace as he would be able to fulfil his mission of saving humanity. He began developing a high ego for being a hero and was even willing to put mankind into peril so that he would be able to saving it again.

Before he was about to put his plan into action, Leo was disrupted by the arrival of the Demon Queen Echidna, and he came to his senses. Leo then proceeded to defeat Echidna and her Demon Army. After winning, Leo was betrayed and denounced by humans due to his monstrous power. Because of this, Leo, under the pretense of developing a deep grudge against humanity and thus seeking to destroy mankind, set out to join Echidna's Demon Army in order to destroy them himself.

Background
Leo was created as one of the Twelve Demonheart Series to save humanity from the first demon invasion in 2060. Over the years, he lived through each generation of human civilization, saving humanity over and over again from the demons. Over the 3000+ years that he lived through, he has grown to be insanely powerful, to the point where can single-handedly defeat Echidna's demon army and became the strongest being in the whole world.

Abilities

 * Crimson Comet: A High level attack magic
 * Twelve Layers Barrier (Stasis): A High level magic which can nullify or seal any magic, regardless of the type and power.
 * Voice Changer: A magic that allows him to change his voice to anybody's.
 * Metamorphosis: A magic for disguise.
 * Clearance: A magic which heals diseases or curses.

Rare Magic

 * Mirage Eye: A magic technique that can send the information that was seen as it is in its eyes to its caster.

Echidna
Initially, Leo saw Echidna as just another Demon ruler to defeat, but when he saw her refuse to allow her army to pillage and kill civilians, he became curios about her. As he defeated her army and the Four Great Generals, his curiosity grew. He chose to join her cause to understand her motives for invading the human world, but she could not forgive him for destroying her army. In his Black Knight Onyx guise, Leo came to understand her true nature, and genuinely desired to help her achieve her dream. He even deemed her worthy of replacing him as the world's protector.

Steina
Despite being his boss, Leo only takes Steina seriously when she gives him an assignment, behaving nonchalantly outside of work. However, he recognizes the immense pressure she under, and does his best to alleviate her workload. He also flirts with her

Lily
Leo first met Lily when she was wandering as an amnesiac, he decided to let her travel with him. When her memory returned and he was forced to defeat her, Lily became obsessed with him. It turns out as her people believe when someone of the opposite sex defeats them, said person is their destined mate. Leo is uninterested in marrying her though, seeing her more as annoying but loveable friend.

Mernes
Leo sees Mernes as someone like himself: unable to enjoy life because of their jobs. After defeating him, Leo encourages him to explore the world as a person rather than an assassin. When tasked with helping Mernes improve his communication skills, he discovers elements of a normal teenager under his silent assassin demeanor, and trusts him enough to open up about his past.

Quotes

 * "Eat, sleep and play, I can laze around as I like here!"

Trivia

 * Leo inherits the power of the Hero through the Philosopher's Stone. Although this doesn't mean that anyone could get the power by simply touching the stone, Leo was able to hold onto the power due to his abundant life experience.
 * Leo is powered by the Akashic Engine (Philosopher's Stone) which serves as his heart.