"Magmadiver" is the tenth episode of the Japanese anime television series Neon Genesis Evangelion, which was created by Gainax. The episode, written by Hideaki Anno and Akio Satsukawa and directed by Tsuyoshi Kaga and Kiroyuki Ishido, was first broadcast on TV Tokyo on December 6, 1995. The series is set fifteen years after a worldwide cataclysm and is mostly set in the futuristic, fortified city Tokyo-3. The series' protagonist is Shinji Ikari, a teenage boy who is recruited by his father Gendo to the special military organization Nerv to pilot a gigantic, bio-mechanical mecha named Evangelion into combat with beings called Angels. During the episode, Asuka Langley Soryu, a girl who is designated as the pilot of Evangelion Unit-02, tries to capture the eighth Angel, Sandalphon, found in the magma chamber of a Volcano in a dormant state.

The episode continues the so-called 'action arc' of the series, making room for humor and teenage tones. The basic plot of "Magmadiver" took inspiration from a documentary called Life: A Long Journey of 4 Billion Years by NHK, and critics and official material on the series found references to trilobites, The Andromeda Strain and previous works by the Gainax studio.

"Magmadiver" drew a 9.5% audience share on Japanese television, the highest for an episode of Neon Genesis Evangelion to date. It received an ambivalent or negative reception from critics, as it was considered filler and full of excessive fan service; the addition of erotic elements primarily used to please the audience. Other reviewers received the installment more positively, praising the humor, the battle against Sandalphon and Shinji's actions.

Shinji Ikari, pilot of the mecha Eva-01, and Asuka Langley Soryu, his fellow pilot deputed to command the Evangelion Unit-02, continue their cohabitation at the home of Misato Katsuragi of the special agency Nerv, deputed to the annihilation of the Angels. While their companions go on a trip to Okinawa, the two pilots remain in the city of Tokyo-3 in case of an enemy attack.

Meanwhile, Sandalphon, an Angel in a dormant state, enclosed in a chrysalis-like cocoon, is detected by the seismographic center of Mount Asama and Misato. Nerv therefore decides to undertake an action to capture the dormant Angel. To do so, Asuka and the Eva-02 are equipped with a special pressure and lava-resistant suit, the Type D equipment. Asuka then dives into the volcanic magma chamber and captures the Angel. After capturing it, however, the Angel wakes up and attacks the Eva. Asuka, exploiting the principles of thermal expansion, defeats the enemy, and Shinji with his Eva-01 rescues her before she can become trapped in the magma.

In 1993, Gainax wrote a presentation document for Neon Genesis Evangelion entitled New Century Evangelion (tentative name) Proposal (新世紀エヴァンゲリオン (仮) 企画書, Shinseiki Evangelion (kari) kikakusho) to find potential sponsor for the series, containing the initial synopsis for the planned episodes. The Proposal document was then published in 1994 and it already included the "Magmadiver" plot. The original plan was for an episode centered on a magma fight to be the eleventh episode and an episode on a Nerv blackout to be the tenth one. During production, however, the episodes were reversed; what was supposed to be the eleventh episode became the tenth, while the draft on the tenth episode's blackout was used for "The Day Tokyo-3 Stood Still". In the "Proposal" document, moreover, the seventeenth episode was also supposed to feature a romance comedy about Asuka's first date; some of the elements of the initial scenario then flowed into the tenth episode, especially in the scene where Asuka goes shopping with Kaji. "Magmadiver" was written by Akio Satsukawa in collaboration with Hideaki Anno, the director of the series, while the storyboards were edited by Anno himself and Tsuyoshi Kaga. Anno also worked on Sandalphon's design. Kaga and Hiroyuki Ishido worked together as the directors, while Shigeta Satoshi served as the chief animator. Takeshi Honda designed Asuka's dress, while Seiji Kio and Mitsumu Wogi worked as the assistant character designers.

Writer Alexandre Marine noted how "Magmadiver" is one of the few episodes which is faithful to the original plan. The basic plot of "Magmadiver", centered on the character of Asuka, the focus of the series' "action arc", was written with a simple structure, featuring the classic beginning-development-end unfolding. The defeat of the Angel is made possible by a creative application of a basic lesson of thermodynamics mentioned in the previous scenes, reprising the classic robot anime plot scheme of the 1970s, in which an element presented at the beginning of an episode becomes useful as a resolution to the concluding fight. For the plot staff also took inspiration from an NHK special called Life: A Long Journey of 4 Billion Years, which aired in Japan in 1994. Life features, among others, the prehistoric animal Anomalocaris, which inspired Sandalphon's appearance.

For the fight against Sandalphon, set in Mount Asama, special water glass was used to create a distortion effect. A distorted cry of an infant was also used for the Angel's vocalizations at the start of the battle. Tomokazu Seki, Junko Iwao, Megumi Hayashibara, Tetsuya Iwanaga, voice actors of several main characters in the series, played unidentified characters for "Magmadiver". Moreover, songs from Lila ~ from Ys, an album by Misato's voice actress Kotono Mitsuishi, were used during the episode. Yoko Takahashi also sang the final theme song of the installment, a cover of the song "Fly Me to the Moon", later replaced with a version named "Asuka Main" in subsequent home video editions.