Only continue reading if you're totally okay with that.
|“||And even though that light we see, ain't the same for you and me. Oh well you'll know when I know, that you and I can even be a thousand light years away. And I'd still love you. Oh, yes I do. I love you.||”|
— The end credit song "1000 Light Years Away" about Casey's feelings for Beatrix
Casey is the special someone of Beatrix back on Earth who will occasionally send letters to her via StarMail during the course of Adventure Mode, revealing some background information about Beatrix, Casey, and their relationship. Their gender is intentionally ambiguous.
|Received Day 1 at noon.|
|Received 48 hours after reading Rise and shine!|
|Received 24 hours after opening your first Slime Gate, or 24 hours after reading My pet cactus if you have already opened a Gate.|
|Received 24 hours after opening two Slime Gates, or 24 hours after reading Re: The big storm if you have already opened two.|
|Received 24 hours after opening the Ancient Ruins plort gate, or 24 hours after reading Re: the... VAN if you have already opened it.|
|Received 24 hours after opening four Slime Gates, or 24 hours after reading New Year's Eve if you have already opened four.|
|Received 24 hours after opening five Slime Gates, or 24 hours after reading Re: Africa if you have already opened five.|
|Received 24 hours after unlocking the Glass Desert, or 24 hours after reading Coming home if you have already unlocked it.|
|Received 24 hours after reading Re: London.|
|Received 6 hours after reading Hobson's last note in The Glass Desert, or 6 hours after reading Re: Life is different now if it has already been read; triggers the End Credits when you Return to Ranch|
Pre 0.6.0 Starmail
- Note: "My pet cactus" is omitted from this list; it was the only one that was not changed.
- 1.0.0 - One final StarMail was added as part of the end of Adventure Mode. Casey's back view can also be seen in the credits.
- 0.6.0 - Changed StarMail messages to make Casey less clingy and remove real-world landmarks from their stories. Another two StarMail messages were added, totaling 10.
- 0.5.1 - Implemented with the first 8 StarMail.
- According to Monomi Park, the end credits song 1,000 Light Years Away is not sung by Casey; the song represents Casey's relationship with Beatrix, but the voice itself is not Casey's. 
- http://forums.monomipark.com/viewtopic.php?f=3&t=4280&p=33663&#p33663 - Nick's response on a forum thread
- http://steamcommunity.com/app/433340/discussions/0/1470840994979491796/?ctp=4#c1470840994980036934 - A Monomi Park dev specifically states this.