After his family is massacred for guarding a legendary martial art, Qin Feng trades ten years of his sanity and half his life for demonic power. For a decade, he lives as a fool under the protection of his senior, Mu Qingcheng, until his family’s enemies return and nearly kill her. With his memories restored and the Demon Seed awakened, Qin Feng rises as a Demon Lord, ready to make his enemies pay.
In the Republican Era, Chinese martial arts boasted Thirteen Ultimate Skills. The greedy Japanese Sakura Martial Society seized twelve and finally took the Qin family's Sky-Measuring Ruler, cruelly killing the protagonist's parents. Overwhelmed with grief, the protagonist swears to slay all his enemies, kicking off a thrilling revenge journey.
Once a legendary martial prodigy, Qin Feng makes a fateful deal: he gains unrivaled slaughter power by embracing the demonic path, paying with a ten-year mind seal and half his lifespan. A decade later, his family is wiped out for defying Dongying, leaving him homeless—until a kind couple takes him in.
Hua Country's 13 ultimate martial arts techniques were plundered by Dongying's Sakura Martial Arts Society. Talented Mu Qingcheng created the 14th technique, Soft Cloud Swordplay. The silly junior brother with godlike strength is bullied, but she protects him. Now, Yagyu Musashi from the society challenges her in three days!
Musashi Yagyu targets Mu Qingcheng's swordplay. Her brothers reject escape, vowing to face Sakura Dojo in three days to defend their martial arts dignity.
Senior Sister sends her seemingly foolish Junior Brother to live with a countryside couple, seeing him as a burden with enemies approaching. To her surprise, he runs over a hundred miles back to stay by her side, refusing to leave. A cryptic prophecy reveals he’s destined to awaken as the Demon Lord, hinting untapped power as they face the Dongying Dojo.
Yagyu Musashi invites Mu Qingcheng to join his Sakura Martial Arts Club serving Japan, tempting her with authentic martial arts and secret manuals. Mu refuses sharply, citing her father’s words and demanding those who harmed Hua people commit seppuku, sparking a tense standoff.
Yagyu Musashi dismisses a junior as an idiot and challenges the renowned Soft Cloud Sword wielder. The eldest senior brother, despite not mastering any ultimate skills, volunteers to fight first to test the enemy's strength, driven by duty to protect his sect and boost Hua Nation martial artists' morale. Another senior brother steps up next.
After the eldest brother's death, the second brother leads his siblings to fight Eastern enemies, vowing to uphold the unyielding Huaxia spirit. Though he teases his fool junior brother, he fiercely defends him from outsiders. As siblings fall in battle, the junior sister fights to avenge them, while the enemy mocks Huaxia's martial arts and prepares to showcase a fused new form.
A Japanese villain flies into a rage, threatening to crush Chinese warriors' spirit inch by inch. He forces the senior sister to submit, but she proudly defends Chinese warrior ethos. The seemingly foolish junior brother rises up, inspiring all warriors to fight back and refuse surrender, igniting a fierce clash.
Arrogant Japanese samurai brutalize Chinese fighters, hurling insults like 'sick men of China' and forcing them to kneel. They plot to humiliate a Chinese woman, sparking desperate resistance and heart-wrenching choices that hook viewers.
In this intense episode, Senior Sister confronts the dismissively labeled 'Fool,' claiming she’ll teach him to love a woman. The Fool fires back, mocking her as a chained mad dog unable to protect loved ones or harm her enemies. Enraged, Senior Sister vows to grind all Japanese scum to dust, sparking a fiery clash filled with bitter animosity and high stakes.
Having regained clarity, the junior brother swears to protect his senior sister who saved and sheltered him for a decade. When Dongying villains strike, he defeats one, attracting the Four Bladesmen—killers of Hua's Thirteen Grandmasters who boast they can counter all Hua martial arts. His sister warns him to flee, and he suspects a link to the Qin family, sparking a tense clash.
When the Qin heir overhears his enemies mocking how his mother was slashed 18 times before dying, he reveals his true identity and vows revenge. Targeted for death, he unleashes hidden martial arts, and when his foe threatens with a powerful martial club leader father, he swears to make the villain taste the agony of losing loved ones.
Qin Feng, branded a demon for practicing demonic martial arts, confronts the Martial Arts Association President who forbids him from slaying Yagyu Musashi. He accuses the president of being Japan's watchdog, ignoring their people's deaths and his senior sister's bullying. Qin Feng vows to protect the innocent and eliminate traitors as a demon, challenging the hypocritical righteous leader.
When a junior brother tries to kill a threatening man, his senior sister intervenes, warning innocent lives will perish with him and stating living in shame is harder than revenge. The man threatens his death will bury Hua Nation, sparking a tense standoff, with Yagyu Musashi’s arrival amplifying the conflict.
Qin Feng spares an ambushing enemy, vowing to claim Yagyu Tajima's life. Senior Sister Mu Qingcheng swears to fight Dongying relentlessly and frets over the toll of Qin's demonic arts. When the Huaguo Martial Association arrives to take Qin, Mu volunteers to go instead, sparking Qin's fierce threat against the Association.
Mu Qingcheng fiercely defends her junior brother Qin Feng, disputing the rigid divide between good and evil. Pressured by the chairman to hand over cultivation methods, she offers her swordplay—only to uncover his secret deal with Lord Yagyu Musashi, a stunning betrayal.
Qin Feng trades his lifespan for demonic power to gain strength. Upon learning his senior sister is captured by the Martial Association colluding with Japanese warriors, he vows to rescue her, while the villains mock him and plot to humiliate his sister.
Humiliated by an 'idiot', a Japanese samurai vents his anger on captured Huaguo wealthy daughters. The disgraced Huaguo Martial Arts President collaborates with him, while a defiant girl pins hope on her junior brother, only to be warned he’ll be torn apart by ambushes.
At Sakura Dojo, vile villains target a charming Chinese woman, spewing vulgar words and plotting to end her life, treating her as a 'wild horse' to tame. As she falls into grave danger, a thunderous declaration echoes: 'Today your lives are mine to claim', heralding an avenger's arrival.