In this game, destroing enemies or other obstacles will produce stellar shaped items.
Collect 1,000,000 of them to unlock this achievement.
Since you can collect several thousand of them in one play (you must be very good at Mamonoro! if you could collect 10K), this is among the most daunting achievement in this game.
But if you have turbo pad, you can collect them automatically in the following way.
1. Set Y-button as curse shot. This can be done in OPTION - CONTROLS - NOROI.
2. In Practice mode, select setting as
STAGE: MISSION4
PLAYER: MAMORU
DIFFICULTY: one star
RANK: 100
LIFE: 4
POWER: 4
TIME: 5:00
3. Start game.
4. Set fire rate for A-button and Y-button to max, hold and fix them with some rubber band.
In this way, you can repeat practice play automatically, collecting 800-1000 items in about one minute's play. For me, it took about 19 hours(!) to collect million. If you've collected some already while unlocking other achievements, it would be done in shorter time.
Note: credit for the original idea of repating practice mode with turbo pad goes to Japanese Achievement Wiki (
http://www12.atwiki.jp/xbox360score/pages/771.html, author anonymous).