Playing an older brother in the film "The Commitment" has prompted Choi Seung Hyun, a.k.a. Bigbang's T.O.P. to think about what it means to be a big brother.

In real life, the singer-turned actor has an older sister but not a younger one. However in his movie role, he plays Myung Hoon, a North Korean student who must abandon his dream of becoming a pianist to become an undercover agent. He does so to protect his younger sister, Hye Ri, played by Kim Yoo Jung. In the film he would sacrifice anything for her.

But in real life, what kind of older brother would he make? While you never know what kind of sister you would wind up with, he can only guess how he would act based on his friendship with co-star Kim Yoo Jung. Even though there was something very mature and serious about the actress, he still felt protective of her.

"If I had a younger sister like Kim Yoo Jung I would probably care for her a lot," said T.O.P. "I would be kind to her and just live a honorable life. I find that there is something deep about the brother-sister relationship."

One thing he would not do is to introduce his little sister to the other members of BigBang.

"They are all cool guys, but the decision has nothing to do with whether they are cool or not," he said with a laugh. "Would I let them close to my family?"

It's best not to mesh different parts of your life, he said.

"If someone made my younger sister cry, our team work could be negatively affected so I would probably not mix family and work."

No need, since when she was asked in an interview which BigBang member she liked best, she said it was T.O.P.

"I like them all, but TOP oppa's voice is attractive," said Kim Yoo Jung. "And, he also works hard at becoming a singer. I like his sincerity."

When his fellow band members showed up to support him during the VIP premiere of "The Commitment," they were all impressed with his portrayal of a big brother.

G-Dragon said that he wanted T.O.P. to show his love for his band members just the way Myung Hoon did for his sister.

Taeyang also admitted to getting caught up in the story and identified with Myung Hoon's desire to protect Hye-Ri.

"During the time he spent looking for his sister, we watched and waited with him," said Taeyang.

"The Commitment" reached number one in box office sales the first day that it was released.