user: Question: Who did he fight in Rumble of the Kings 6?
Columns: ['Res.', 'Record', 'Opponent', 'Method', 'Event', 'Round', 'Time', 'Location']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Win', '5-0', 'Yusuke Kawaguchi', 'TKO (punches and elbows)', 'Rumble of the Kings 6', 1.0, '3:18', 'Stockholm , Sweden']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Event" = 'Rumble of the Kings 6';