Here is the full list of all 43 Sword Art Online: Lost Song achievements.
Complete a side quest, Extra Quest, or Multiplayer Quest with a party consisting of Kirito and Asuna.
Complete a side quest, Extra Quest, or Multiplayer quest with a party consisting of Kirito, Klein, and Agil.
Complete a side quest, Extra Quest, or Multiplayer Quest with a party consisting of Silica, Lisbeth, and Leafa.
Raise Asuna, Yuuki, Rain, and Sumeragi's OSS to level 100.
Complete a total of 100 side quests.
Befriend Sumeragi.
Learn every possible Sword Skill, Magic Skill, and Special Skill for a single character.
Raise a weapon's Enhancement Level to its maximum.
Obtain Excalibur.
Complete a total of 10 side quests, Extra Quests, and/or Multiplayer Quests with a party consisting of any single character.
Raise a single Sword Skill to level 500. *OSS included.
Go to the festival with all the game's heroines. "This's a sweet scoop!"
Complete Lisbeth's side story. "We're going to forge a lot of memories together, whether you like it or not."
Complete Asuna's side story. "Stay with me forever, Asuna."
Complete all main story chapters. "We still have a lot more gaming left to do!"
Create a party that includes your own custom character.
Reach the story chapter "The Two Idols."
Complete Sinon's side story. "Sinon is an indispensable part of this team, and an important friend."
Reach the story chapter "The Twilight of the Gods."
Raise a single Magic Skill or Special Skill to level 500.
Complete Silica's side story. "I won't tell anyone what happened here today."
Have more than 1,000,000 Yuld.
Reach the story chapter "The Dark World."
Complete an Extra Quest without taking damage.
Reach the story chapter "Intertwined Desires."
Have the character you are controlling reach 0 HP and become a Remain Light.
Reach the story chapter "Lies."
Resurrect a party member who has become a Remain Light.
Reach the story chapter "Battle of the Knights of the Tri-blade."
Defeat 1,000 enemies over the course of the game.
Reach the story chapter "A Paradox of Light and Darkness."
Reach the story chapter "The Red-head in the Shadows."
Complete Leafa's side story. "I hope that I'll always get along with Sugu."
Reach the story chapter "The Youthful Goddess."
Complete your first side quest.
Defeat 5 or more enemies at the same time with a single attack.
Reach the story chapter "The World of the Black Fairies."
Reach the story chapter "Fairies in the Sky."
Log into ALfheim Online.
Earn all trophies. "You are an excellent fighter. The best I have ever seen."
Complete a total of 100 Extra Quests and/or Multiplayer Quests.
Collect 100 different weapons, not including shields.
Collect 50 different accessories.