Optimus(Ren Force in the Japanese game) are basically the replacement for Knights in White Knight Chronicles: Origins each with their own advantages, unlike White Knight Chronicles the transformation uses the unity gauge instead of AC. The accents of the different Optimus armor is based on the wearer's Chroma.
Energy- Focuses on Ren Force attacks and charges the unity gauge faster.
Brave- Has high chances of getting criticals, useful for attackers.
Defence- Has high defense and regenerates HP.
Sorcery- Focuses more on spells and amplifying them
Sorcery Form
Defence Form
Brave Form
Energy Form