Family Determination! (Japanese: がんばリーリエ！決意の家出！！Lively Lilie! A Determined Runaway!!) is the 51st episode of the Sun & Moon series, and the 990th episode of the Pokémon anime. It first aired in Japan on November 23, 2017, in New Zealand on March 1, 2018, and in the United States on March 31, 2018.
Our heroes are in shock after Lusamine’s disappearance through an Ultra Wormhole, and they want to help get her back. But Gladion insists it’s a family matter, and he and Lillie set out on their own rescue mission. The Pokémon School class still wants to help, though, so Kahuna Hala directs them to the Altar of the Sunne on Poni Island. Meanwhile, nearing the altar, Gladion and Lillie encounter a Totem Kommo-o! With Snowy and Silvally, they defeat the Dragon-type Pokémon. Then, when the siblings rejoin the rest of our heroes, Ash again tries to convince Gladion to let everyone help. And when Lillie agrees, Gladion finally understands…
Following Lusamine's abduction by Nihilego, everyone is in shock. Upon being confronted, Faba tries to pin the blame on Lusamine as Lillie and Gladion vow to save their mother. Professor Burnet can't guarantee they can successfully reopen the Ultra Wormhole so they'll need to find another way. Checking on Nebby, Professor Burnet wonders whether it evolved and suggests Ash keeps looking after it. Returning to the mansion, Ash heads home as Lillie goes to her room. Lillie changes her outfit and returns Snowy to its Poké Ball as Gladion comes in. Gladion knows a way to open an Ultra Wormhole and is leaving without Lillie but gives in when Lillie asks to join him. They leave the mansion, riding on Silvally.
The next day at school, Ash shows his classmates Nebby and fills them in on what happened the previous day when Lusamine was abducted. Professor Kukui arrives with Hobbes and reveal that Gladion and Lillie have disappeared. They decide to visit Hala and seek his advice. Hala informs them of a legend which leads Ash to remember his dream and reveals what happened, leading Hala to mention the Altar of the Sunne. Realizing they need to ask Solgaleo for help, they head to Poni Island. Lillie and Gladion have reached Vast Poni Canyon as they continue towards the Altar of the Sunne. Hobbes has borrowed a boat for the group from Wicke and they set sail for Poni Island.
Lillie and Gladion continue on their journey and Gladion uses information from Aether Pardise research to find their way. He orders Silvally to move the three starter Pokemon statues in the correct places for the door to open. When Lillie tries moving one of the statues, tall spikes appeared. They reach a room where they encounter a group of Jangmo-o, Hakamo-o and a TotemKommo-o. With help from Snowy and Silvally, they are able to defeat them but the roof starts caving in. They are saved by the arrival of the others when the gang quickly destroyed the debris fall but Gladion isn't happy at their arrival. Gladion is persuaded to accept their help and they continue their journey and arrive at the Altar of the Sunne where they find the Guardian deities waiting for them.
In the original preview for this episode, Snowy is colored pink instead of white when Gladion and Lillie were running from the falling debris in the cave. However, in the episode proper, the error was fixed.