In June 2044, the Robotech Expeditionary Force (REF) fleet gathers at Moon Base ALUCE for its final attempt to drive the alien Invid from the Earth. This time, the REF has important technological advantages thanks to the help of the Sentinel races; the Karbarrans provided the industrial resources to construct this armada, while a secretive and highly advanced cybernetic race known as the Haydonites have provided advanced technology including Shadow devices, which make REF ships invisible to Invid sensors, and Syncro-Cannons, which are significantly more powerful than the REF's earlier weapons. The REF fleet is led by newly completed SDF-4 Izumo, a Super Dimensional Fortress over 1.3 km (0.8 miles) long under the command of General Gunther Reinhardt.

The Pioneer Expedition was a mission to confront alien forces in space to prevent interplanetary war on Earth. It took place concurrently with the 2nd and 3rd Robotech wars. The expedition was led by Lisa Hayes aboard the SDF-3, which was launched in 2022 in search of the Robotech Masters. The mission soon became preoccupied with the liberation of worlds under the control of the Invid Regent. In June 2030, the final battle of the Second Robotech War caused a release of the spores of the Invid flower of life across Earth, which soon attracted the Invid. In 2031, the Invid, under the control of the Regis, invaded Earth. The United Earth Forces (including the elite Army of the Southern Cross) had been severely weakened by the Second Robotech War and were only able to offer limited resistance. In less than a week, the Invid seized control of the planet and began utilizing the human population for slave labour and scientific experiments. In 2038 and 2042, the REF sent the 10th and 21st Mars divisions to try to retake the planet, but both ended in complete failure. It was only with the third attempt in 2044, which involved all available REF forces (now equipped with new technology known as new Reflex Weapons and Shadow Techno Fighters obtained from the Haydonites) that the Invid were dislodged from Earth.

The Hashira Training conducted by the Hashira is a special training session that aims to improve all Demon Slayers' abilities and physical health. The training is split between the Hashiras. First, the Sound Hashira, Uzui Tengen conducts training on basic stamina. Then, the Love Hashira, Kanroji Mitsuri handles flexibility training and the Mist Hashira, Muichirou Tokito, deals with the quick movement training. The Snake Hashira, Obanai Iguro, then focuses on sword skill revision, followed up by the Wind Hashira, Sanemi Shinazugawa, who handles pounding training and finally the Rock Hashira, Gyomei Himejima, who trains muscle reinforcement. The Insect Hashira, Shinobu Kocho does not take part in the training. The majority of the Demon Slayers view the training session as an everlasting trip in hell, with the exception of Tanjiro Kamado and Inosuke Hashibira who see the session as a chance to improve themselves. As a general rule, Hashira must take part in each other's training sessions. It is considered a win-win situation for both the Hashira and the Demon Slayers as even the Hashira get to improve due to being constantly attacked by wave upon wave of juniors ranked lower than themselves.

Tanjiro, Zenitsu, and Inosuke go on their first mission together and venture to Mount Natagumo. Too afraid to go up the "spooky mountain" with Tanjiro and Inosuke, Zenitsu stays behind. Tanjiro and Inosuke encounter a mountain laced with spider webs and controlled by Spider Demons. These Demons have already dispatched countless Demon Slayers, forcing Kagaya to send in the Hashira as reinforcements.