Goku enters the Demon Realm's 2nd World in the 10th episode of DBD. The episode starts with Kuu & Arinsu in the courtyard of the Supreme Demon King's Castle in the Demon Realm's 1st World and Kuu challenges Tamagami 1 for the Demon Realm's 1-Star Dragonball. Tamagami 1 (voiced by Alex Hom) asks if Kuu is certain he wants to fight him and once Kuu confirms this, Tamagami 1 accepts Kuu's challenge. As Kuu battles Tamagami 1, Goku's group reaches the Yellow Sir Warp in the Demon Realm's 3rd World and are able to successfully enter Sir Warp's pocket dimension; they are also successful in tricking a small Sir Warp when he notices they aren't members of the Gendarmerie despite using a Gendarmerie airship by Panzy claiming they have family members who are members of the Gendarmerie.
Upon reaching the 3 color-coded hatches in Sir Warp's pocket dimension, Shin points out that the fact that the Gendarmerie airship they took hasn't been reported stolen yet gives them a chance to sneak their way into the Demon Realm's 1st World which Panzy agrees is a valid point. Goku, on the other hand, points out that that they'll need to travel to the Demon Realm's 2nd World in order to obtain the Demon Realm's 2-Star Dragonball which Glorio confirms to be true. Goku thanks Glorio (who has to remind Goku what his name is when Goku forgets and calls him "Grillo") for taking his side in this debate. After Shin reassures Goku that that Dende's kidnappers aren't likely to kill Dende because they didn't when they had the chance, Goku feels even more confident about heading to the Demon Realm's 2nd World.
Vegeta, Piccolo, Bulma & Hybis are heading towards the Yellow Sir Warp in the Demon Realm's 3rd World after reclaiming the airship with a "mid-size passenger load". Piccolo bringing up that Dende is currently a baby and that the Earth's set of Dragonballs will need time to recharge leads to Vegeta conceding that Goku may have a point about using the Demon Realm's set of Dragonballs to undo Gomah's wish. Bulma takes on a moment to relish how her skin feels after Gomah's wish and she thanks Hybis when he compliments her skin. Vegeta takes issue with both Hybis asking Bulma to be his girlfriend (while also saying he doesn't "mind sharing" with Vegeta) and Bulma considering staying as a kid; when Bulma suggests letting her stay a kid while undoing Gomah's wish for everyone else affected by it, Vegeta insists they undo Gomah's wish on both of them…which Hybis takes as a sign of what Vegeta finds attractive and Piccolo noting Hybis "read [Vegeta] like a book". Back in the Demon Realm's 1st World, Kuu continues to battle Tamagami 1.
Goku's group have arrived in the Demon Realm's 2nd World (which has a green sky, much like Planet Namek) via a Blue Sir Warp much to Gomah's dismay and Panzy marvels at how it differs from the Demon Realm's 3rd World while Shin admits his memories of when he was previously here are starting to come back to him. Glorio notes that the Demon Realm's 2nd World doesn't have any heavy air like the Demon Realm's 3rd World did which means the Gendarmerie airship can go even faster and he also notes that Tamagami 2 isn't far from their current location. Shin's returning memories lead to him asking if there still any Krakens around and Glorio confirms this to be the case. Shin takes the time to explain to Goku that Krakens are giant water inhabiting creatures that will attack anyone who flies too close to the water surface while Panzy admits that she's heard many stories about the Krakens.
Suddenly, 5 Gendarmerie airships ambush Goku's group and Goku is eventually forced to fly outside to take down the 5 Gendarmerie airships personally. Back in the Demon Realm's 1st World, Gomah & Degesu use the magic monitor to watch this unfold and they're both surprised by how powerful Goku is even after being turned back into a kid which leads to Gomah ordering all remaining members of the Gendarmerie to return to the Demon Realm's 1st World immediately. The ambush caused the airship Goku's group is using to drift towards the water surface…which leads to a Kraken attacking the group. Goku's group waste no time escaping the Gendarmerie airship…only for Panzy to return to retrieve the Demon Realm's 3-Star Dragonball before the Kraken eats it; fortunately, Goku is able to save Panzy before the Kraken eats the Gendarmerie airship much to Gomah's dismay. Goku, Shin, Glorio & Panzy are forced to fly themselves now but Shin suggests they wait for Vegeta, Piccolo, Bulma & Hybis to eventually arrive in the Demon Realm's 2nd World…and the Demon Realm's Namek is nearby which Shin notes can act as the perfect waiting place.
Back in the Demon Realm's 1st World, Kuu continues to battle Tamagami 1…only for Kuu & Arinsu to both realize that Tamagami 1 has the clear advantage in this fight. Back in the Demon Realm's 2nd World, Goku's group arrive on the Demon Realm's Namek and Goku notices how it bares a strong resemblance to Universe 7's Namek (as well as New Namek); Shin suspects that the Namekians who originated from the Demon Realm took some Ajisa Trees with them to plant on their new home planets in the Mortal Realm as the reason for why the Planet Namek(s) of the Mortal Realm resemble the Demon Realm's Namek which leads to Goku noting how the Namekians who originated from the Demon Realm would've been especially devastated had they known Frieza would eventually blow up Universe 7's (1st) Planet Namek. Goku begins to feel hungry and is disappointed that the Kraken ate the Manpuku Dumplings & food they had on the Gendarmerie airship…only to remember that he still has the bag of Medi-Bugs on his person. After offering some to the others (who all decline), Goku eats a Revive Bug which despite tasting bad does restore his stamina as advertised while also helping to alleviate his hunger.
Shin notices just how abandoned the Demon Realm's Namek is and Glorio explains how after the Namekians who originated from the Demon Realm left, the water became polluted. Suddenly, Goku senses the energy signatures of Vegeta's group and decides to go see them to guide them to the Demon Realm's Namek; Panzy is confused by how Goku knows about the others' arrival when he can't see them and Shin briefly explains how Goku can sense energy signatures while Glorio muses how Goku is "an odd one". Goku finds the airship with a "mid-size passenger load" shortly after Bulma admits the Demon Realm's 2nd World looks nicer than she expected and he tries to warn the group about the Krakens…only for a Kraken to attack them. Fortunately, Hybis is able to fly the airship away from the Kraken before it has a chance to eat the group.
Back in the Demon Realm's 1st World, Kuu accepts that he can't defeat Tamagami 1 and concedes defeat. Tamagami 1 returns to his original position while Arinsu & Kuu fly off in an airship…all before a few members of the Gendarmerie arrive to checkout the source of recent noise. Arinsu harshly states how unimpressed she was with Kuu and plans to fire him but Kuu urges her not to be so hasty by pointing out his impressive speed would make him great for running to the store (while also saying he has great singing talent). Meanwhile, Goku guides the airship with a "mid-size passenger load" to the Demon Realm's Namek which leads to the 2 groups reuniting.
Like with Bulma, Piccolo has to point out to Goku that this is his 1st time being on the Demon Realm's Namek although he does admit there is still a feeling of familiarity as he looks at the home of his ancestors. Bulma takes notice when Panzy calls Shin by his real name of "Nahare" and recalls Planet Kaishin (the Glinds' home planet) is located in the Demon Realm's 2nd World which leads to Goku providing Bulma the necessary context. When Bulma asks Shin why most of the Glinds left the Demon Realm, Shin proceeds to reveal that there was a good Supreme Demon King (who had blue skin in contrast to the red skin Dabura had) that entrusted a "Super Majin" named "Rymus" (who bares a strong resemblance to Grand Zeno the Omni-King from DBS) to create the Mortal Realm/the multiverse. Various inhabitants of the Demon Realm immigrated to the Mortal Realm's various universes to "stake their claims" and Rymus entrusted a select group of Glinds to oversee the multiverse's settlers & aid in the multiverse's development by having them take the position of the Supreme Kais of the multiverse while most of the Glinds "settled on a planet near Rymus" should Rymus ask for their help, as well; Anato (Universe 1's Supreme Kai), Ogma (Universe 5's Supreme Kai), Fuwa (Universe 6's Supreme Kai), Iru (Universe 8's Supreme Kai), Gowasu (Universe 10's Supreme Kai), Cae (Universe 11's Supreme Kai) & Agu (Universe 12's Supreme Kai) are shown onscreen alongside Shin as he explains how the position of Supreme Kai came to exist. When Bulma asks if all living beings have ancestors who originated from the Demon Realm, Shin clarifies that there are living beings whose ancestors originated from the Mortal Realm (such as Saiyans & Humans).
Shin continues to explain that travel through the Mortal Realm/the multiverse & the Demon Realm via Sir Warp used to be more easily accessible but Dabura's father, Abura (who looks like a fatter version of his son), had placed the current restrictions on Sir Warp out of fear of the possibility of an invasion from the Mortal Realm; Shin also clarifies for Bulma that he was still in the Demon Realm when Abura was Supreme Demon King shortly before he was chosen as a Supreme Kai. Goku recalls how the Glinds are born from 1 of 5 Glind Trees and Shin confirms this is true but adds that all 5 Glind Trees have died out; Bulma realizes that means it's only a matter of time before the Glinds become extinct and Shin somberly confirms this is true. When Hybis brings up how Degesu & Arinsu are Glinds while complimenting Shin for being smart, Panzy recalls how Degesu & Arinsu are Shin's siblings; Hybis shows some sympathy towards Shin after hearing this while describing Degesu & Arinsu as jerks which is a sentiment Shin completely understands. Bulma asks Shin if he wants to revisit the Demon Realm's Kaishin while they're in the Demon Realm's 2nd World but Shin acknowledges there isn't anything left to see on the abandoned planet anymore and suggests they continue heading towards Tamagami 2 which Vegeta agrees with an aggressive enthusiastic manner; as the group board the airship, Bulma suggests Glorio pilot the airship which Hybis agrees to after Bulma assures him her suggestion is because Glorio seems more familiar with the Demon Realm's 2nd World while this is Hybis' first time here. The episode ends with the group unaware of the fact that Neva had been watching them while they were on the Demon Realm's Namek.
I found it rather amusing how Goku ended up spending 7 episodes in the Demon Realm's 3rd World since that number is the amount of Dragonballs for most sets. Besides entering the Demon Realm's 2nd World, the most notable detail about this episode is the lore about the creation of Mortal Realm/the multiverse. Given his strong resemblance to Zeno, I'm guessing Rymus is Zeno's predecessor and maybe even Zeno's father (or, at least, ancestor). The existence of the good Supreme Demon King also shows that not all the rulers of the Demon Realm were evil. It was a nice touch having some of the DBS Supreme Kais be shown while Shin was explaining how the position came to exist; the knowledge that the Glinds will eventually become extinct makes me wonder what that will mean for any future Supreme Kais in the multiverse. In the end, Kuu wasn't powerful enough to defeat Tamagami 1 much to Arinsu's dismay which makes me wonder if Kuu will be getting a "sibling" in the near future. It makes sense that Neva would be on the Demon Realm's Namek and the episode's ending suggests he's preparing to "formally" greet them. With this episode, Toonami has now aired the first half of DBD.