Hello World (Japanese: ハロー・ワールド), stylized as HELLO WORLD, is a 2019 Japanese animated science fiction romantic drama film directed by Tomohiko Itō from an original screenplay written by Mado Nozaki. Produced by Graphinica and distributed by Toho, the film is set in a futuristic Kyoto where a high school student named Naomi Katagaki encounters a person claiming to be himself, who time-traveled from 10 years in the future to save a classmate named Ruri Ichigyō.

The film stars Takumi Kitamura, Tori Matsuzaka, and Minami Hamabe. In December 2018, Itō announced that he would be directing the film, along with Nozaki and character animation designer Yukiko Horiguchi, making it his first film outside Sword Art Online series that he was known for directing.

Hello World premiered in Kyoto on September 11, 2019, and was released in Japan on September 20. The film grossed over $25 million worldwide, with critics praising the direction and animation. The film received novelization, two manga adaptations, and an anime spin-off.

Set in Kyoto 2024, the Japanese government has made plans to collect and preserve the city's natural architecture and culture through drones in real time, storing all its data in an infinite-capacity quantum computer known as Alltale. Naomi Katagaki is an indecisive high school student living in Kyoto who harbors a love for reading. One day after school, a mysterious yatagarasu steals his library book and in an attempt to get it back, he meets a strange man that appears out of nowhere. This man, whom only Naomi can see, is revealed to be himself from 10 years later, now grown up and an adult. The adult Naomi explains that he has accessed Alltale from the real world outside in order to change the recorded past and save Naomi's to-be girlfriend, his classmate Ruri Ichigyō, after she was unfortunately struck by lightning at a fireworks festival and rendered comatose. The teenage Naomi decides to call his adult self 'Sensei' and agrees to help, as his adult self has limited capabilities as an avatar within Alltale. Sensei then gifts Naomi a special power, God's Hand, which manifests from the yatagarasu as a translucent gloved hand, to allow him to create anything as long as its chemical and physical structure is not overly complex.

Consulting his own diary, Sensei leads Naomi to slowly gain Ruri's affection and they eventually fall in love. On the night of the incident, Naomi refuses to invite her out for the festival and remains outside her house per Sensei's orders. They realise that due to this being a world within Alltale, Sensei's interference has caused its Homeostatic System to kick in. Bots in the form of kitsune men appear attempting to correct the data, transporting Ruri and Naomi to the site of the incident. Summoning a black hole, Naomi erases not only the kitsune men, but also the stroke of lightning that would have hit the tree Ruri was originally supposed to have waited at and hence the accident, successfully rescuing Ruri and rewriting the data.

In a twist of events, Sensei suddenly reclaims God's Hand and teleports Ruri away before disappearing. Naomi is shocked as he realizes that Sensei's plan was to recreate Ruri's original mental state in Alltale so that the data within could be synced with Ruri's own comatose mind in the real world, enabling her to wake up. Returning, defeated, to the city, Naomi is suddenly faced with thousands of kitsune men — an effect of Sensei deciding to reboot the system after all data relevant to Ruri's existence has been rewritten. The system then automatically starts filtering parts of data to keep and those to be erased, causing the space within 2024 Kyoto to shift and for red auroras to appear in the sky. Naomi, recalling how Ruri was teleported away in a similar fashion, jumps into the redness. He awakes in a virtual space to the yatagarasu, who assures him that he is not dead and promises to help him save Ruri, manifesting God's Hand for him once more.

Meanwhile, in the real world, Sensei embraces Ruri, who has woken up from a coma. However, kitsune men soon start appearing around the room targeting her, Sensei realized his world is also a world within Alltale. Teenage Naomi warps to Ruri's hospital room and prepares to bring her to the staircase outside Alltale's complex, which has the optimal spatial coordinates for them to return to their original world. With help from Sensei, they manage to outrun the kitsune men and Ruri returns to her time via a portal created by God's Hand. The kitsune men, shifting their targets to the two Naomis, transform into a horrible gigantic creature that overpowers Naomi's strength. In the last moment, Sensei sacrifices himself, knowing that there can only be one Naomi and thanking his past self for letting him see Ruri smile again, wishing for him to always be happy. Inside the Alltale Management Facility, Alltale is successfully shut down after its data goes haywire and begins to duplicate itself. Alltale logic system has been deactivated which makes it possible for a parallel world to happen inside Alltale. In tears, Naomi returns to Ruri and the two share a kiss. As the data has been written and rewritten beyond recognition, Naomi greets a parallel world ahead of him and Ruri.

In the final scene, adult Naomi awakens atop a human civilization on the Moon, to the overlapping voice of the yatagarasu and an adult Ruri, implying that Naomi fell into a coma after saving Ruri due to the injuries from failing to enter Alltale in his previous attempts and now it was adult Ruri transferring Naomi's memory from Alltale to the real world.