Valkyrie Plains is the first stage in Stories of Legend Sub-chapter 25, Scars of War.
A whole wave of Shibaliens will appear which is spammed throughout the level with other doge variants appearing as bosses.
With the beginning of the chapter 25 of the Stories of Legends, you should have the treasures Aqua Crystal and Plasma Crystal from the Into the Future Chapters, as alien units will start to appear as a threat.
First, stall the first Shibaliens, then build up a stack of attackers.
Doge will spawn, along with many more Shibaliens. While the Doge has an enormous strength magnification, it still isn't high enough to be consider him much of a threat. Just use a couple of midrange attackers such as Cameraman Cat and he should die in seconds (all while meatshielding properly, of course). A similar process can then be repeated for every wave.
If you can get the second wave of Shibaliens just behind hitting range at the base then you can destroy the base without killing them which prevents the succeeding bosses from spawning, making you win the level.
- This stage has the (currently) strongest Doge Darks in the game, even stronger than the ones in Star Ocean (for 1 star, that is)
- This is the first Stories of Legend stage where an Alien enemy appears