Adan will be officially unveiled by Betis on Wednesday and, despite the club being 10 points below 17th place in the La Liga table, he is excited to be moving to Estadio Benito Villamarin.
"The main reason I've decided to come is the feeling this club gives me," he told reporters. "After a game against Real Madrid I got the feeling this was a very big club. I'm hugely motivated.
"I'm aware of the situation that the club is in, but I had to take this step. The important thing is to be realistic. The situation is difficult but the first thing is to give everything on the pitch."
Adan could make his debut in Sunday's home match against Espanyol.