How does Overdrive work?

At the end of Chapter 5, you earn the ability to activate Overdrive after accumulating 3,000TP. What are the mechanics of this? Including:

• What does the big number in the middle count? What does having a higher number achieve?
• What determines how long it lasts for, and can it be extended?
• What determines if your partners contribute to the Overdrive?
• Can partners activate their Overdrive by themselves?
• Does "chaining" art colours (like Xenoblade Chronicles' chain attacks) have an advantage?
• Certain bonuses seem to be tied to following one specific art colour with another. Are they random, and what are the bonuses?

Any other mechanics I've missed too.

Solution 1:

Overdrive greatly improves your combat abilities for a short time by doing the following:

• Reduced cooldown times allow you to use your Arts more frequently.
• Adds a tertiary cooldown, which further enhances the power of your Arts beyond what is possible with the secondary cooldown. The secondary cooldown is represented by a green ring around you Art's button; the tertiary cooldown is white.
• Secondary and tertiary cooldowns continue ticking down for all Arts, regardless of which weapon type you're currently using.

When you activate Overdrive, the big button in the center changes appearances and shows you both the "Overdrive Counter" and the "Overdrive Time".

Overdrive Counter

It is represented by the big number in the center. The counter increases with each successful hit from an Art during Overdrive. The higher the counter goes, the greater the bonus you get from Overdrive. Support (green), Debuff (purple), and Aura (blue) Arts do not increase the counter.

The color of the Overdrive Counter changes depending on which Art you used last. Changing the color triggers a Color Combo with various effects. The effect depends on which color replaced which. The effects include:

• Double Overdrive Counter Bonus: Doubles the amount by which the Overdrive Counter increases whenever you use an Art.
• Appendage Damage Up: Increases the damage you do to enemy limbs.
• HP Recovery: You recover a little bit of HP.
• Debuff Effect Time Extended: Debuffs inflicted on enemies last 35% longer.
• EXP Bonus: Increases the amount of EXP earned.
• Class EXP Bonus: Same as above, but affects your class EXP instead.

Overdrive Time

The small bars on the right of the button (highlighted in red in the screenshot) represent the time you have left in Overdrive. When it runs out, Overdrive ends. You can increase the number — and thus how long you stay in Overdrive — by accumulating another 3000 TP and initiating Overdrive again before it runs out.

When your party members reach 3000 TP, they may activate Overdrive of their own. When multiple party members enter Overdrive, special effects will trigger:

• 2 members: Soul Voices occur more often.
• 3 members: Gain 50 additional TP per hit when using an Art.
• 4 members: All party members receive the buff "Super Armor", which reduces all damage taken by 50% and grants immunity to debuff effects, such as Stagger, Topple, Knockback, Launch, and Flinch.