-They currently worked for the detective agency located in Splatsville shortly after they leave Squidbeak Splatoon years ago.
-Despite them leaving, they've been given hero gear replica as a parting gift from the Squidbeak Splatoon. Whether the one who gifts them hero gear replica is presumably Marie or Cuttlefish is still unknown.
-The hero headphones were heavily modified by the detective agency after the recruitment of Agent 4 (Shown above).
-Both were considered role models of the detective club and the detective agency because of their studious attitude. But Castor himself never finds such praise necessary and often times, pushes himself too hard and overly critical of everyone even himself. He is an expert in navigating through most places and analyzing things. He also deeply cares for his sister's wellbeing.
-Callisto on the other hand, finds happiness in basically travelling around whether it was with Castor or just her alone. She became good friends with Agent 8 (named Oz) after their encounter in the deepsea metro. Both Callisto and Oz keep in touch by sharing messages and their interests after the events of Octo Expansion. She is also terrified of Agent 3 at the same time, admire him as a role model.
What Castor and Callisto think of others:
Marie
Castor: Marie huh? For an idol beloved by many, I cannot wrap around that attitude of hers especially how she treats Callisto by calling her 'Agent Snore' when we first meet her. For some reason I still can't stand her attitude until now. Especially what she said to my sister.
Callisto: I think Marie just has a different side to her especially dealing with many fans and her job as an agent. We're basically on good terms now. I hope that she still does well. I kinda miss her. I just hope that Castor never starts a fight with Marie if we meet each other again.
Oz (Agent 8)
Castor: Callisto seems to be in a good mood when seeing him. I hope that he's doing well in the surface. I wish him nothing but happiness, finding the light at the end of the dark tunnel. I hope we could find a way to meet him again.
Callisto: You don't know how much I appreciate Oz as one of my best friends along with my brother!
There's so many cool things about Oz that I want to tell you!
One time, He sent me a picture of Inkopolis tower over at the chat and it looks pretty! We're going to visit Inkopolis plaza real soon, it looks fun!
Cuttlefish
Castor: We met this man at the deepsea metro, he seems to be brimming with energy despite his age.
Callisto: Is he the grandpa of Agent 3?
Castor:....I don't think that's his grandpa,
Callisto. He's more of a mentor to me.
Callisto: Oh...My mistake!
Still both of them are super cool though!
Agent 3
Castor: Agent 3....I can't help but feel sadness about his fate. The one who risked his life bringing the Great Zapfish back to Inkopolis. Only for him to not be remembered and suffered at the hands of the deepsea metro. forgotten by many, remembered by the few. My only wish is that he will be cherished and remembered for his accomplishments.
Callisto: A-Agent 3 is s-super scary especially when he is brainwashed by that phone! And worse of all, he nearly caught me with that sunken scroll on the way to the surface. B-but, he saved Oz from that blender, right?
I h-hope he's nice to us now that's he's free from that phone's influence..
The night skies above lit up with glimmering stars, each star is as precious as a crystal. 
