A Beautiful End (美しき終焉 Utsukushiki Shūen) is the twenty-first and penultimate episode of Ultraman X.
The episode starts with Daichi conducting a new experiment for three days straight with Asuna coming to visit because she is getting worried about him. Daichi is trying to find out the source from where his mother's voice came from at the same space-time singularity that their lab was taken away during the Ultra Flare incident. According to him, the process is similar to fossil fragment finding and that an ancient relic his dad found at this spot could mean a clue to an important piece of the puzzle and tries to contact them.
Meanwhile, near the moon, Wataru and Mamoru in the Mare Australe, the newest Musketty model, search for the source of the Dark Thunder Energy, talking about how they plan on defending the Earth with love after pointing out that this Musketty isn't equipped with an ultimate beam cannon.
Back on Earth, Hayato, Takeru, and Chikari discuss where to eat for the lunch run then play rock paper scissors for it while Rui and Doctor Guruman try out a Fanton specialty, yogurt noodles, and talk about selling it on Earth and naming it after Rui, to the doctor's protests. The three then get a call from the UNVER HQ in Geneva, saying that the source of the Dark Thunder Energy is approaching the Earth at a close pace.
Wataru and Mamoru are told about this and notice that the space energy levels are getting to level zero, which is bad. Daichi finally contacts his mom before being told that there is an unidentified light heading towards Earth. Doctor Guruman explains that the source of the DTE is something that doesn't exist and it is considered that light.
The strange object finally reaches Earth and lands in the Xio base in Nevada, annihilating it. Ultraman X immediately identifies the threat as Greeza and insists that he must talk to everyone at Xio directly. He does so via everyone's Xio Devisors and explains that Greeza targets the life energy of planets and leaves nothing in its wake. He also reveals that he was the one who followed him to their solar system after Greeza destroyed three life-plenty planets and presumably defeated him by pushing him into the sun but Greeza has survived. He only attacks the monsters because they are abundant in life energy which is why he attacked Nevada - because it has the largest containment of Spark Dolls on Earth. So now he is heading toward the second largest... in Tokyo.
Xio agrees to cooperate with Ultraman X and begin a 20 kilometer evacuation of the Xio base. Meanwhile, in the Pacific airspace, Xio USA launches Perseus missiles at Greeza but he dodges them all and destroys all the vehicles. Hayato departs in the Sky Musketty after talking with his dad, and Doctor Guruman and Rui work on the system's energy shield while Tachibana activates the final defenses. As Greeza arrives, Daichi has Asuna pull over in the Xio Porthos and reveals to Asuna that he is Ultraman X. Stunned, she tells the rest of Xio as X immediately transforms into his Exceed X form and fights Greeza. Asuna then realizes Cyber Gomora to help out the Ultra and Doctor Guruman activates the Hyper Energy Shield.
Unfortunately, even with the combined efforts of Ultraman Exceed X, Cyber Gomora, and the Sky Musketty, Greeza gained the upper hand, shot down the Musketty and emits a strange soundwave that disrupts the technology and brought suffering to the both of them. Daichi, however, doesn't give up and X tries to use the Exceed X Slash on Greeza only to be absorbed by him, leaving only his Color Timer standing, much to the horror of everyone.
Daichi's Monster Lab
This section was unavailable in this episode. Probably due to X and Daichi "dying" this episode.
- Daichi Ozora (大空大地 Ōzora Daichi): Kensuke Takahashi (高橋健介 Takahashi Kensuke)
- Asuna Yamase (山瀬アスナ Yamase Asuna): Akane Sakanoue (坂ノ上茜 Sakanōe Akane)
- Wataru Kazama (風間ワタル Kazama Wataru): Yoshihiko Hosoda (細田よしひこ Hosoda Yoshihiko)
- Hayato Kijima (貴島ハヤト Kijima Hayato): Ukyou Matsumoto (松本享恭 Matsumoto Ukyou)
- Mamoru Mikazuki (三日月マモル Mikazuki Mamoru): Hayato Harada (原田隼人 Harada Hayato)
- Rui Takada (高田ルイ Takada Rui): Haruka Momokawa (百川晴香 Momokawa Haruka)
- Takeru Yamagishi (山岸タケル Yamagishi Takeru): TAKERU
- Chiaki Matsudo (松戸チアキ Matsudo Chiaki): Chiaki Seshimo (瀬下千晶 Seshimo Chiaki)
- Sayuri Tachibana (橘さゆり Tachibana Sayuri): Sarara Tsukifune (月船さらら Tsukifune Sarara)
- Shotaro Kamiki (神木正太郎 Kamiki Shōtarō): Yuu Kamio (神尾 佑 Kamio Yū)
- Ultraman X (ウルトラマンエックス Urutoraman Ekkusu): Yuichi Nakamura (中村悠一 Nakamura Yūichi)
- Alien Fanton Guruman (ファントン星人グルマン Fanton Seijin Guruman): Yasunori Matsumoto (松本保典 Matsumoto Yasunori)
- Ultraman X (ウルトラマンエックス Urutoraman Ekkusu): Sakaekei Iwata (岩田栄慶 Iwata Eikei)
- Alien Fanton Guruman (ファントン星人グルマン Fanton Seijin Guruman): Hiroyuki Fukushima (福島弘之 Fukushima Hiroyuki)
- Cyber Gomora (サイバーゴモラ Saibā Gomora): Akira Okabe (岡部 暁 Okabe Akira)
- Greeza (グリーザ Gurīza): Yoshiki Kuwahara (桑原義樹 Kuwahara Yoshiki)
- Ultraman X
- Ultraman Exceed X
- The prop used to display Xio USA ships were simply reused from Xio Musketty in its mid-transformation sequence to Space Musketty. Furthermore, Xio Japan's Base's rocket launchers were added onto said props as minor alterations.
- The scene in which Greeza's pieces fall toward Asuna was a re-enactment of Zetton's demise from episode 39 of the original Ultraman, in response to Hirotoshi Kobayashi contributing Zetton's design to Greeza.
- This episode was later featured in Ultraman New Generation Chronicle episode 14, "Invasion! A Beautiful End!!".