The Japan international said: "I am very happy to be part of this great team. I just saw the field, I already played here once, but it is spectacular as the Ciudad Deportiva. I hope to have a good season both individually and collectively.
"I hope I can have a great season, let's see how things are happening.
"I chose Villarreal because it is the best option, that's what I, my family and representatives think, so now I have to prove it."
Kubo added: "Yes, there were other offers, but this was the best, that's why I came here. I'm only focused on Villarreal, I don't think about other things. I'm 100% at the service of Villarreal, as I did last year at Mallorca."