The South Korea international, who featured at the World Cup, returns to the Liberty Stadium after spending the previous campaign at fellow Premier League side Sunderland.
He started in Swansea's 4-0 friendly win at Plymouth Argyle last Sunday and played an hour of the 2-0 win over Exeter City on Tuesday.
The 25-year-old midfielder, who helped Swansea win the League Cup in 2013, recognises that there is much competition for a starting berth at the Welsh outfit but is confident he can be a valuable asset to the team.
Speaking to the club's official website, he said: "It's good to be back. After the World Cup I had three weeks off before I joined up with the team.
"Now I want to get as fit as I can so I can prove myself in the team.
"It was a very good time for me at Sunderland. I showed that I can help the team, so I hope to do that at Swansea [too].
"There is always competition for a position here - that goes for every player.
"If you play well then you will play, if not you will be on the bench or not involved, but I will push myself as hard as I can.
"Everyone in this team has great quality. Every season Swansea get stronger and stronger.
"With the mix of new players along with the players here last year, it will be a good balance."
