Since you asked to — I’ll assume you want a design for a new gameplay or narrative feature suitable for that version. If you meant something else (a feature list, a bugfix, a walkthrough, or a fan expansion), just let me know.
Collecting all echoes in a chapter unlocks a 「Despair-Break Form」 — a temporary, powerful but unstable transformation with unique art and voice lines. Magical Girl Luna--39-s Misfortunes -v1.09- By Nama...