The first chapter basically calls Husky a "princess"...
A lot of Husky's actions towards Cooro has the other come off as a Tsundere.
Special note of when the group decide to leave Cooro behind with a lady and her husband because he seemed happier there. When he ultimately comes back to the group, Nana makes note of Husky in particular being sad at the thought of Cooro not journeying with them anymore. When Cooro gets excited and asks Husky if that were true, Husky refuses to answer and angrily hits Cooro with his stick.
When Nana joined the group, Husky was very upset and said it was 'all her fault he couldn't keep the promise [he] made with [Cooro]." (the promise being to travel with him if Cooro untied him from a large pole.) Obviously, he wants Cooro to get rid of Nana so he can stay with him. Cooro then tells him to just forget the promise and leaves, and Husky gets very depressed.
He has a staff called the 'Cooro Punishing Stick'. Enough said.
Nevermind that they're kids. Husky being constantly mistaken for a hot girl generally leads to lots of interesting situations, but particularly in the first chapter, Cooro either deliberately hits on Husky, or is very oblivious that That Came Out Wrong. Even though he knows Husky's a boy.
Senri
Senri licks Cooro’s arm after he starts bleeding in the same way he had done to Rose earlier which was assumed to be done out of attraction. He even notes that their blood tasted yummy.
Cooro
Cooro and Shadow's interactions in chapters 9 and 10 are so alarmingly subtext-heavy that it makes you wonder if Mukai was intentionally playing it up as a parallel to a romantic relationship. Cooro meets Shadow while the latter is testing out a glider and is accidentally knocked out by said glider. Shadow nurses him back to health and Cooro offers to help him with the glider so that he can help out his family easier. But then Shadow finds out about Cooro being a +Anima with wings and due to a misunderstanding, he immediately believes he's been being played for a fool and, more or less, "breaks up" with Cooro. Cooro's reaction is a surprisingly deep depression that leaves him sulking on the ground and hiding in his wings for a while. Upon his friends discovering him in this state, Cooro's dialogue sounds like someone fresh from a break-up.
Senri: (places a hand on Cooro's forehead) Hurt. Nana: What? You're hurt?! Cooro: Uh-uh. It doesn't hurt anymore...I'm just...kind of...tired... Husky: Cooro? Cooro: I wanted to stay with him longer...but he told me to go away. We were getting along so well...he evengave me cheese.
When he sees that Shadow's in danger and flies off to rescue him, he ultimately earns Shadow's forgiveness and the two become friends again.