Rain-ysh, It is an American slang expression, but I don’t think it is popular enough to call it an idiom. Go into one’s dance…To begin a prepared line of pleading, explanation, selling, seduction, etc: Examples: -He went into his dance, but she wasn’t convinced -The salesman went into a song and dance about the value of a good life insurance policy. -Earlier in the evening, I could already sense where Devyn’s mind was heading. Hanging out with Janel and her hubby, he WENT INTO HIS DANCE about his latest decorating challenge: painting the old masonry walls of his apartment white. -The squirrel would shamelessly go into his dance and begging routine to get peanuts from me

I'm not quite sure what the situation is. Is Tanaka a part of a dance team? If so, "go into my dance" might be a shorter way to say "go into my dance practice" or "I'm about to start dancing" I never hear that phrasing tossed around in english a lot, however...

i have never heard of it before =s