A husband only approves those knee socks!
Kyoya has convinced Josef to stay with them for a long time!
Of course, Josef was a free man that enjoyed adventures mostly solo. It was just his disposition, and it was something that Kyoya was aware of. He was also aware that Josef was similar to him when it comes to the parties.
Their goal is not to fight or do missions from the adventurer guild, but to focus on their own stuff. Of course, it doesn't mean the adventurer guild is useless or anything like that. The perks of being adventurer affiliated to the top guilds were just too good to be missed.
Regardless of that, everyone has their own path.
Though the parties could be diverse, it's often best to have at least some small goals connected to every party member.
For such a reason, Kyoya had to find a goal that would connect him to Josef. He could bluntly say that he wants to find more fire-related origins, but Josef already found a sufficient share of fire piece to his sacrifice for Lord Aron.