I have just read it and haven’t gotten the time to throughly reflect on it since I did it so fast, but to me, that have the whole story so fresh in mind, this seems beautifully written.
When I think of it, the manga has been pointing out since day one how death is distressful and how one should value their life above all. Only those who cherish it can become shinki. They portrait it as if facing the demons that were left in a past life is the downfall of any spirit, since it is stained with the longing for life. So to be honest, Yukine isn’t being a brat, to me. He is going down the path that is expected of any shinki when faced with their past lives. He was even doing fine with Yato’s absence, until that shadow bestowed upon him.
All characters seem to me very faithful to their nature and personalities. Yukine’s need for care and attention has also been pictured before, and then he learned that love doesn’t come in form of material belongings. He learned to trust himself more, to be at ease and calm even when Yato has bad behaviors such as going missing or losing control, even when the thing he eagers the most is Yato’s approval.
Also, motivations are on point because the aggravating event which is Yato abandoning him simply can’t be helped. The character’s grown past his selfishness but he can’t help it since what he is doing is exactly to try to protect his shinki from the exact fate he is going down right now.
At the background, the story plays over and over with the concept of good and evil, pointing out all the gray areas on every creature, being it a god, a human, a shinki, an ayakashi or both. Ebisu being the one who walks the middle line and embraces both good and evil and Yato being that who crosses the lines, without turning away from his nature to “cull the herd”, which to me opens up to interpretation to who that herd might be.