Mission 59: Collect shining shards
Collect three shining shards.
Collect four shining shards.
Roxas is sent to Twilight Town to collect Shining Shards for item synthesis (as said in the briefing). These are collected by defeating Guardians. There is also a Tailbunker attacking Roxas as he goes about this mission.
In order to open this mission, you must talk to Xigbar sometime between Days 194-197. He wants you to destroy thirty enemies with a Limit Break. Doing so before the end of Day 197 and talking to him a second time opens this mission. If you miss it the first time through but finish the game, it will open as a holo-mission.
Make your way down to Tram Common. Ignore the Tailbunker unless you find it completely necessary to fight it. Scout around to find three Guardian Heartless. Destroy those three and collect the shining shards which they drop. This will make the message "Mission Complete" appear. If you want to finish the mission fully, find a fourth Guardian and destroy it. Collect its shining shard. Mission complete.
Eliminate three Guardians in the Tram Common area to procure Shining Shards, then return to the dark corridor. Use Thunder magic against each to quicken the battles, consuming Ethers as needed. Upon entering the Tram Common, follow the curve to the left and up the stairs to take out the first. Then cross the "bridge" to fight the next one on the rooftop before dropping over the south side and taking out the third.