So, what skill rings should I go for if I focus on Hero twin guns style?
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There aren't many rings Hero will be using due to their weapons/etc.
The rings tend to be more "universal" for the Hero depending on what conveniences you want as the Hero doesn't get too many changes otherwise with the rings so my suggestions are the following:
Atomizer Lovers (L)
Mate Lovers (L)
Mag Excitement (L)
Party Toughness (L)
Defensive Techniques (L)
Critical Strike (R)
Valor Emblem (R)
In order to create the Critical Strike and Perfectionist rings you must have all three of the original rings (MEL/RNG/TEC versions) and then create a Compound Ring out of the +20 versions of all three rings. The Valor Emblem is created through the Extreme Quest "Elite Training: Tainted Border" where you will get the resources to craft and upgrade the ring depending on the class you play as. The rings are universal and only change in appearance depending on the class you created it for (such as the "Hero Ring" showing its sigil and emblem but is still usable on any other class). I would only really recommend the Valor Emblem if you already maxed out your opportunities for critical rate (such as if you have a Fighter involved in your class combination who cannot use Critical Strike as a ring). If you prefer to have more consistency Perfectionist definitely works as well.
If you have twelve-star units (which you should upon reaching Level 75 for the Stella Wall units) you can install three additional (L) rings alongside one you have equipped. I personally use Atomizer Lovers, Defensive Techniques, Party Toughness, and currently Early Riser as a placeholder for leveling up rings. On the right side I use Critical Strike (R) because it is a ring you definitely want for maximizing damage especially with the S-Class Special Abilities in use.
The only way you can actually change or modify gameplay elements of the Hero is through the weapon potentials of special weapons like Dual Bird (restores 30 PP and gives an automatic regeneration effect over time after performing a perfect dodge) or the Demonia weapons which have varying effects that amplify the Hero's gameplay.