Sea Mauville (Japanese: シーキンセツSea Kinsetsu) is a decrepit research facility in the Hoennregion, located to the north of Route 108. The second part of the structure can only be accessed by using Dive and contains the Scanner.
Sea Mauville includes both the decrepit platform itself as well as the water area and sandbar outside of the facility; the northern exterior can only be accessed by travelling underwater inside the platform using Dive.
In Omega Ruby, at the end of the beam that extends a significant distance west and upwards from the platform, a portal appears if the player has the Clear Bell. Interacting with this portal will initiate a battle with Ho-Oh. In Alpha Sapphire, at the control desk in the submerged control room, a portal appears if the player has the Tidal Bell. Interacting with this portal will initiate a battle with Lugia. If the player fails to catch the Legendary Pokémon in their initial encounter with it, they will be able to battle it once more each time they enter the Hall of Fame.
After defeating or capturing Kyogre/Groudon, in the first (southeastern/lower-left) room of the northern (right-hand) dry corridor, when the player enters the room, the message "It feels as though you're being watched" will be displayed. If the player then stands in the top-left corner of the room and opens a menu (such that they cannot see the overworld), they will see the Odd Keystone upon returning to the overworld, initiating a battle with Spiritomb. This will also occur if the player saves at the top-left position and reloads; in this case, the player cannot continue without battling Spiritomb. As with Ho-Oh/Lugia, the player can re-battle Spiritomb each time they enter the Hall of Fame.
Sea Mauville was a facility commissioned by Greater Mauville Holdings and led by Wattson to extract the natural resources of the ocean. Members of the staff included Captain Stern, Dock, Professor Cozmo's father Raizoh, and Cap'n Salty. Due to several incidents, such as the closure of New Mauville, the facility was closed. After its closure, an environmental survey discovered that the ruins had created a unique habitat for Pokémon and plants, such as mangroves, which only grow there and in Mossdeep City. Because of this, its demolition was canceled, and the ruin was revived as a natural preserve.
"There is a worn-out sign. Sea Mauville's 10 slogans for a cheerful and fun workplace."
"01. Say good morning very loudly."
"02. Don't bring Pokémon to your workplace."
"03. Always arrive on time. Always stay late."
"04. Lay your life on the line in safety checks."
"05. Take joint responsibility for teamwork."
"06. Obey your superior's orders absolutely."
"07. Maintain top quality. Give up your sanity."
"08. Worship and praise the founder."
"09. Don't expect time off before you retire."
"10. No need to think. Just work unceasingly."
"There's a crumpled piece of paper inside. "Sea Mauville Company Song" is written on it."
"1. The daybreak shines on Route 108. Wake up, our towering fort. For the bright future Hoenn, We won't take our days off. Dig through, dig out great energy. Ah, Sea Mauville, Sea Mauville, Sea Mauville."
"2. The bright light shines on Route 108. Intensely shiny, our fort. Swear your selfless devotion. Unionization is out of the question. Dig through, dig out great energy. Ah, Sea Mauville, Sea Mauville, Sea Mauville."
"3. Darkness descends on Route 108. Tonight again sleepless, our fort. Drive away our competitors. We won't take our overtime pay. Dig through, dig out great energy. Ah, Sea Mauville, Sea Mauville, Sea Mauville."
"There's an old note at the back of the cabinet with broken glass."
"Finally, the date of closing has been decided. I can't say thank you enough to Stern, who invited us to his shipyard when we would have been left adrift. Dock, who's done a dirty job, and I can both start with a clean slate. The only way we can repay him is to support his business with our skills."
The document is found in a file cabinet in Room 2. The text of the document differs depending on whether Omega Ruby or Alpha Sapphire is being played.
"The file labeled "CONFIDENTIAL" contains stained documents. The documents have dates way before you were born."
"De— Sec— Investi— —port"
"The develop— on new —rgy turned out to be true. The ene— that uses —kémo— bio—rgy is called —inity Ener—."
"Investi— Report on Wa—"
"A series of actions related to cancellation of the —w Mauvil— Proje— tur— out to be true. I recom— prompt discip— action against him as a traitor to our group."
"Do— Team E Leader, —ative Group —"
"—von Secret —gation Re—"
"The —ment on new ene— turned out to be true. The —rgy that uses Po—on's —ene— is called Inf— —gy."
"—gation Report on —son"
"A series of actions related to cancellation of the New —lle Project —ned out to be true. I —mend prompt —linary action against him as a traitor to our group."
The bookshelf that the player examines in order to fight Spiritomb holds papers describing that Raizoh Cozmo was held responsible for losing an Odd Keystone that was donated to the Sea Mauville by the Oreburgh Mine in Sinnoh.
"The file folder holds a stack of ragged papers."
"Official Statem— of Apolog—"
"I, —izo— Co—mo, am respon— for the los— of the Odd Keystone dona—d...by the Oreb—gh Mine..."
"The rest is too damaged to make out..."
"In the dusty bookcase are old papers covered in detailed statements and records of payments made. The text is blurred in places and hard to read."
"Name: Ra— Coz—o"
"The rest is too damaged to make out."
"It's a tattered clipping from an old magazine cover. On the cover is a young lady who looks like Lisia."
"Termination of New Mauville Project Officially Announced at Last! Serious Talks Begin about the Closure of Sea Mauville! Cries of Concern Erupt from Staff Members Working at Sea Mauville! Greater Mauville Holdings Reps Remain Tight-Lipped about the Issues! Project Leader Wattson Weighs In on Problems Plaguing New Mauville!"
"The rest of the magazine has been torn away..."
The man with no power may be the same as the one in Apartment 11 in Mauville Hills.
"It's an old, hide-bound notebook."
"The damage caused by the cancellation of the New Mauville project has been catastrophic. As a member of the management, much of the blame and the debts will fall upon me. But that will be little consolation to the employees working under me who will lose their livelihoods. I couldn't do a thing for them... I'm a man with no power... Protecting nature and Pokémon and the environment... It's great as an idea. It's a fine ideal to aspire to. And Wattson is a great man for dreaming of it all. But cruel reality and the organization that I must try to preserve have dashed those dreams. I couldn't do a thing for him... I'm a man with no power..." This is the last page with writing on it. Other pages have been torn out."
"There are dirty papers inside the cabinet..."
"Sea Mau—nal Newsletter #389"
"We ha— a new winne—he monthly slogan—mpetition! It's—alty—the lea—Storage Unit No. 1— ith— Don't dirty the seas with pollution and dumping! Dirty your uniform with sweat and hard work! In recog—of his win, Cap'n Sal—will—ceive a Rocky—met and—yperior! —everyone will kee—slogan in the—hearts and—as they giv—re all again—s month!"
Five letters, a photograph, and a drawing are found in the northeastern (lower-right) room in the northern (right-hand) dry corridor:
"How are you? Are you working really hard? I'm doing well. I'm doing all my homework, and I'm helping at home, too. Mommy's working hard and makes us dinner every night. Do you have to work this weekend? Are you going to come home? If you come home, take me to see the star show, OK?
It looked like another letter, but it's a drawing. The drawing is of a boy's face, and written next to it are the words "I love you, Daddy."
"How are you? Are you working really hard? I was sad that you didn't come last weekend. But Mommy didn't seem so sad. She went out with her friend. I finally got that telescope that I've been wanting. It was from you, wasn't it? Thanks, Daddy. I really, really wanted it. I like looking at the sky, Daddy. When I look at the stars, I wonder if you are looking at the same stars, too. Let's look at the stars together, next time you come home.
"How are you? You aren't working too hard, are you? You never come home anymore. I'm worried if you're OK. Mommy goes out with her friends a lot. It seems like fun, so I guess she's doing OK. The Shelgon that you gave me evolved the other day. But I liked it better when it was a Shelgon and it looked like a Meteorite. Salamence was kind of a letdown, so I asked a friend to trade it for his Solrock. I'm sorry, Daddy. I know it was a present, but I think Solrock is cooler. When it gets dark tonight, I'm going to look at the stars again. I'll think of you when I do.
"I was really, really happy to get to meet you the other day. It was so fun playing together again and going to see the star show, too, even if it was just the two of us. It was sad that Mommy couldn't go, and even more sad when you and Mommy fought that night. I'll study hard, just like you told me, and I'll be a good boy, so don't fight. But let me keep watching the stars, even if I have to do all my homework, too. When I grow up, I want to be a professor and study the stars.
"Thank you for writing to me. I'm doing really well here, so please don't worry about me. I hope I'll see you again someday. I dream about it all the time. I brought the telescope you bought me to our new house. Please don't work too hard, Daddy. I hope you are OK. I will always, always love the stars, and I will always, always love you.
"P. S. I'll give you my Hi Skitty doll. Please take care of it for me."
It looked like another letter, but it's a photo. There's a little boy holding a telescope, with a woman beside him, looking bored.
Due to the rotation of the camera upon stepping on the platform from the southern exterior, the player needs to press left on the D-pad or circle pad to move north, with all other cardinal directions rotated accordingly. While the camera is not oriented this way while the player is in the southern exterior, it is while in the northern exterior.
Sea Mauville cannot be accessed without Surf, so all items located here require Surf to obtain.
At the bottom of the northern (right-hand) staircase—approximately one tile away from the north (right) railing and three tiles beyond the end of the stairs—after catching or defeating GroudonOR/KyogreAS
Sea Mauville appeared in Narrowing the Chaser Chase!, where it served as the site of a Project MewTrial Mission, revealed to be a battle royale amongst multiple Project Mew challengers, including Goh and Horace. Besides the other Trainers, the challengers also had to survive hordes of Pokémon unleashed on them by Danika. Ultimately, Goh and Horace were left as the last Trainers standing, and although Horace tried to forfeit in Goh's favor, Goh encouraged him to actually battle him. The battle ended in Goh's loss, making Horace the winner of the mission, although Goh also received some tokens for finishing second.
The Sea Mauville debuted in PS601. Mr. Stone had Sapphire and Emerald taken there as part of an operation to prevent a meteoroid from crashing into the planet. Mr. Stone had Mr. Briney transport machines known as the Absorbers to the Sea Mauville, where they were placed inside of the facility.
After resting for the night, Mr. Stone and Steven began their operation. After putting Chic and Sceptile on the Absorbers, Sapphire and Emerald Mega Evolved their Pokémon. Immediately afterward, Mr. Stone and Steven activated the Absorbers, which then began the process of draining the life energy of Chic and Sceptile, much to their Trainers' horror. The life energy was transferred into a machine known as the dimensional shifter, which was to be outfitted to a rocket that would be launched at the meteoroid in order to create a warp hole that would transport it to another location.
Shortly after the process was finished, the area was attacked by Zinnia and a group of Team Magma and Team AquaGrunts in order to stop the operation. The group fought Zinnia and her allies in order to protect the shifter from being destroyed, but it and Sapphire eventually fell into the hoop of a wild Hoopa, which sent them to another location. With the shifter gone, Zinnia took her attention in stealing Steven's Key Stone, but she was stopped by the arrival of Ruby, who offered up his and Emerald's Key Stones instead. Zinnia accepted the offer and left with the Key Stones, but after her departure, Ruby revealed that he had secretly managed to snatch a special scroll from her. Ultima later revealed that the scroll contained the essence of a move called Dragon Ascent, acting as a sort of primitive TM.
An old magazine found at Sea Mauville features "a young lady who looks like Lisia" on its cover. It is possible that this person is Lisia's mother, Wallace's sister.
Both the Prima game guide and game data contain rematch data for Mysterious Sisters Scall & Ion that cannot be accessed in regular gameplay due to Dive (and thus the Mind Badge) being required to find their room key. The battle, which would have been available after the Feather Badge like another rematch here, would have featured a level 34 Chingling and a level 33 Gardevoir.