Here is the full list of all 64 Metal Slug Defense achievements.
Conquer all stages in Area 1: "SOUTHEAST ASIA"!
Conquer all stages in Area 2: "EAST ASIA"!
Conquer all stages in Area 3: "AFRICA"!
Conquer all stages in Area 4: "CENTRAL ASIA"!
Conquer all stages in Area 5: "DR MOUREAU'S ISLAND"!
Conquer all stages in Area 6: "OCEANIA"!
Conquer all stages in Area 7: "NORTH AMERICAN SOUTHERN"!
Conquer all stages in Area 8: "SOUTH AMERICA"!
Conquer all stages in Area 9: "NORTH ASIA"!
Conquer all stages in Area 10: "SOUTH AFRICA"!
Conquer all stages in Area 11: "WESTERN EUROPE"!
Conquer all stages in Area 12: "NORTH AMERICAN NORTHERN"!
Conquer all stages in Boss Area 1: "WEST ASIA"!
Conquer all stages in Boss Area 2: "NORTH AMERICAN NORTHWESTERN"!
Conquer all stages in Boss Area 3: "EAST EUROPE"!
Conquer all stages in Boss Area 4: "NORTH ASIA NORTHEASTERN"!
Conquer all stages in World2 Area 1: "SOUTHEAST ASIA"!
Conquer all stages in World2 Area 2: "EAST ASIA"!
Conquer all stages in World2 Area 3: "AFRICA"!
Conquer all stages in World2 Area 4: "CENTRAL ASIA"!
Conquer all stages in World2 Area 5: "DR MOUREAU'S ISLAND"!
Conquer all stages in World2 Area 6: "OCEANIA"!
Conquer all stages in World2 Area 7: "NORTH AMERICAN SOUTHERN"!
Conquer all stages in World2 Area 8: "SOUTH AMERICA"!
Conquer all stages in World2 Area 9: "NORTH ASIA"!
Conquer all stages in World2 Area 10: "SOUTH AFRICA"!
Conquer all stages in World2 Area 11: "WESTERN EUROPE"!
Conquer all stages in World2 Area 12: "NORTH AMERICAN NORTHERN"!
Conquer all stages in World2 Boss Area 1: "WEST ASIA"!
Conquer all stages in World2 Boss Area 2: "NORTH AMERICAN NORTHWESTERN"!
Conquer all stages in World2 Boss Area 3: "EAST EUROPE"!
Conquer all stages in World2 Boss Area 4: "NORTH ASIA NORTHEASTERN"!
Area 1: Free "MARCHRIUS DENNIS ROSSI"!
Area 2: Free "TARMICLE ROVING Ⅲ"!
Area 3: Free "FIOLINA GERMI"!
Area 4: Free "ERI KASAMOTO"!
Area 5: Free "GIMLET"!
Area 6: Free "RED EYE"!
Area 7: Free "TREVOR SPACEY"!
Area 8: Free "NADIA CASSEL"!
Area 9: Free "WALTER RYAN"!
Area 10: Free "TYRA ELSON"!
Area 11: Free "RUMI AIKAWA"!
Area 12: Free "SV-CAMEL"!
Boss Area 1: Capture "ABUL ABBAS"!
Boss Area 2: Capture "ALLEN O'NEIL"!
Boss Area 3: Capture "DONALD MORDEN"!
Boss Area 4: Capture "MARS PEOPLE"!
World2 Area 1: Free "RALF JONES"!
World2 Area 2: Free "CLARK STILL"!
World2 Area 3: Free "WHIP"!
World2 Area 4: Free "LEONA HEIDERN"!
World2 Area 5: Free "UTAN"!
World2 Area 6: Free "HYAKUTARO ICHIMONJI"!
World2 Area 7: Free "LILLY"!
World2 Area 8: Free "CYNTHIA"!
World2 Area 9: Free "MARY"!
World2 Area 10: Free "HEIDERN"!
World2 Area 11: Free "MADOKA AIKAWA"!
World2 Area 12: Free "ZOMBIE MARCO"!
World2 Boss Area 1: Capture "ABUL ABBAS"!
World2 Boss Area 2: Capture "ALLEN O'NEIL"!
World2 Boss Area 3: Capture "DONALD MORDEN"!
World2 Boss Area 4: Capture "MARS PEOPLE"!