Yoshihiro Togashi the creator of Hunter x Hunter is married to the creator of Sailor Moon, Naoko Takeuchi, so in Sailor Moon Crystal (2014) when usagi is in the arcade you see a video game named greed island, and in hunter x hunter baby alluka is playing with a toy usagi and tuxedo mask
Mito is played by Gon's voice actress' real mom.
Killua has the most screen time in show, even more than Gon.
At or around episode 17 Killua's voice, in the American dubbed version, is noticeably deeper than previous episodes.
The entire anime itself can be considered the story of Gon and Killua. In the manga following the Chimera Ant Saga, it focuses on Leorio and Kurapika now.