I've heard that to play this, I would need a diatonic B flat harmonica but I don't really know. Please help!
is played on a Bb diatonic (SP20), with tabs. But it does use a bunch of bends (3' 3'' 4' 6''). Of course if playing along you could use any key of harmonica; it would just sound higher or lower with the same tab.
A chromatic lets you play the accidentals without bending.
I've learned from other questions that tremolo harmonica is popular in Asia for its ability to handle melodies, but I don't have any experience with that kind.
Looks like you asked the same thing on http://seldane.proboards.com/thread/6009/harmonica-used-sora-kiseki and got some good answers.