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Katherine Sunday (also spelled Catherine Sunday) is the main assistant and only other main character in Endless Ocean, residing on the Gabbiano, the player's trusty boat.

Behavior and Personality

Katherine is friendly and amiable, warming up to the player right away. She frequently offers advice and directions, either through talking conversation on the boat, notes on her notice board on the cabin window, or communication via a radio somewhere on the player character's suit.

Though she cannot swim and fears swimming (hence why she wears a life vest all the time), there is a camera on the player's diving suit somewhere that she receives video feed from, which allows her to see all that they see. As such, she can provide them with directions, instructions, advice, knowledge, and other comments.

Katherine is very intelligent and intuitive, and appears to have the ability to understand animals on a basic level; she can read their body language and vocal signals to translate what she believes they are saying, as was first displayed in the presence of an African Penguin that climbed up onto the player's boat. She also has extensive knowledge about artifacts and oceanic archaeology, as can be surmised from the surprisingly extensive information she provides the player with whenever they recover a salvage item of importance or discover a unique area. Nonetheless, she frequently contacts people who know more than she does in order to give the player more information.

She seems particularly uneasy about the Deity Idol, a small figurine described as "ominous" in the player's footlocker.

Her most common nickname is "Kat" - a coworker and friend of hers, Douglas Banner, refers to her by it whenever he talks about her over email.

Some of Katherine's dialogue, namely her usage of the word "mate" as a way to refer to the player, might hint that she is from Australia or the UK; it is known through in-game dialogue that her father was European, so the latter seems more plausible.

Warning.png Spoilers for Endless Ocean ahead!


Katherine was fascinated by ocean life from a young age. Her father, Patrick Sunday, was a scientist and sailor who died whilst searching for the Ancient Mother (presumably by drowning). Katherine's goal is to find the White Mother and finish her father's quest, but her inability to swim held her back until the player character came along. It is unknown where her fear of swimming came from, although it can be assumed that it might have had something to do with her father's death.

In-Game Dialogue (Examples)
At one point, Kat will be leaning against the railing of the Gabbiano, humming quietly to herself and lost in thought, when she's taken off-guard by the player approaching:

"ūüéĶ ...Mmmmmm hmmmmmm‚ĶūüéĶ

Whaaa! Stop sneaking up on me!

What, that song? Oh, it's nothing. It's just…just a song I like.

My mom used to sing it to me when I was a kid. This'll sound weird, but...I couldn't remember it for the longest time. But once I came back to Pelago, I couldn't get it out of my head. Actually, I remembered it the moment I saw the ocean.

Yeah, so, that's it. That's my story. I'm just thinking about the song and mom and other memories..."

At another point, the player will return from a dive to find Kat lounging in the deck chair aboard the Gabbiano. She seems to be in a state of melancholy:

"Hey. How's it going?

Me? Naw, I'm fine. I'm just...thinking. Deep thoughts, right?

Hey, do you ever think about your life mission? You know, like...your destiny or whatever? I think everyone has a purpose. you just have to find it.

I was born here in the Pelago Commonwealth. 'Course, you probably knew that… My mom was native, but my dad was from Europe. I loved it here, but I had to leave when I was a kid. There were...problems. Yeah, so I grew up overseas and just kept trying to get back here, and…

And so, yeah! Here I am! Twenty years later, and I'm right back where I started! Anyway, that's why I've been thinking about my life mission.

...I'm sorry, I'm.... I'm talking like a crazy person again, huh?

Sorry, I just… I spend so much time alone, and I…

Look, just forget it, OK? I'll stop rambling. Promise."

After the player receives an email from Alfred Thorman rejecting a request for some highly-specialized - and therefore expensive - equipment, they exit the cabin to be greeted by an agitated Kat:

"Yeah, I saw Thorman's email! So what?!

...I mean… Wait, that's not what I meant.

Look, I know that's some pretty crazy equipment. And I know it isn't really necessary for the work we're doing. I've been thinking about my life mission, and I think…

Just...trust me on this one, okay? I'll take care of it, I promise. It's my problem anyway!

...I shouldn't have said anything."

After this, she goes silent and refuses to say anything more to the player, which is a sharp contrast to her usual chatty, friendly nature. The only way to get her to open up is to read an email from Doug offering a hint about her behavior, which directs the player to look in Green Garden. Finding Patrick's Pocket Watch, which used to belong to Kat's father Patrick Sunday, will prompt Kat to explain everything.


  • Katherine has a fairly large fan base. Her kind and friendly personality was often seen as a very welcoming factor to the game. When Endless Ocean: Blue World was announced, many people were eagerly anticipating her return however she was replaced with a similar looking shorter girl named Oceana. In early screenshots Oceana was mistaken for Katherine without her glasses, some people even thought it was Katherine's cousin. Her removal from the sequel angered many fans and Oceana does not appear to have received the same amount of popularity.
  • Katherine is often criticized for the uselessness of her comments. Normally when talking to her, she comments upon the current mission the player should focus on, or she makes a randomized comment or states a random fact. Game reviewers stated that Katherine looked too robotic and took away from the game's atmosphere. The critics also complained about her pointless dialogue. For example, when the Idol treasure is reconstructed she says something along the lines of "I have a feeling something bad will happen if I reconnect these pieces... Oh well, let's do it anyway".
  • Some speculation has arisen as to why she was not featured in Endless Ocean 2. One rumor is that she was fired for being unable to swim and be of more use, whereas another rumor suggests that her findings concerning White Mother have led her to fame and fortune, meaning she no longer needs her job as a secretary.
  • There's a theory that Katherine is a mermaid. Supposedly, she won't touch water because if she does, her mermaid tail will form and her secret will be revealed. This is really the only evidence to the theory, so it's highly unlikely. By this logic, Jean-Eric would have transformed into a merman after the accident that left him unable to dive, so this theory has only a miniscule amount of merit or backing.
Warning.png Spoilers for Endless Ocean end here.