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.
The 25-year-old recognises the competition for a starting berth - which has been heightened since the signing of Gylfi Sigurdsson from Tottenham - but is confident he can be a valuable asset to the team.
"It's good to be back. After the World Cup I had three weeks off before I joined up with the team," he told the club' official website. "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."