i don't know where i read it, they said that chun didn't use his own voice in hana kimi...
well, it was his real voice!!!
if you want a proof, you can watch some behind the scene videos of hana kimi in youtube, sometimes it took several takes to make him deliver some tongue twisting lines...
another thing, it's true that he lacks fluency in mandarin, or should i say, he doesn't understand and can't speak mandarin before, that's why in TOKYO JULIET, he lip sync his lines, and someone will deliver it for him. they do this because it's chun's first time to act with a foreign language to use...
THAT'S FINAL!!!
CHUN DID LIP SYNC HIS LINES IN TOKYO JULIET BUT NOT IN HANA KIMI!!!
(its understandable, right?)