For those that prefer watching a video version:
What is Synchro Device?
Synchro Device is a system that will allow you to boost a NIKKE’s level to match the highest 5 leveled characters you have. This makes it so you don’t have to worry about leveling any new NIKKE’s you obtain that may suit your preferences and needs!
Now this may get confusing so pay attention! The current 5 highest leveled NIKKEs will be shown in the menu, where the lowest level of the NIKKE will be chosen in order to determine the current level you can boost your other NIKKEs to. If they are all equal level, then the equal level instead will be chosen.
You can access the option in your Outpost.
One thing that the in-game description of this feature doesn't tell you is that whenever you place a character inside the Synchro device (but not as one of the top 5 characters), she will be leveled beyond her level cap.
This means that the single copy of Scarlet or Harran that you rerolled for, won't be stuck on level 80 (the initial level cap) until you get a dupe. Instead, you will use all your resources on 5x SR characters - getting dupes for them is super easy and with just 2, you can increase their level cap from 80 to 160 (they can't go further using 'normal' means). Then you throw your shiny SSR into the Synchro device and it will be leveled up to the lowest level of your top 5 - even beyond the level cap!
Also, you don't waste any resources leveling those SR, because at any moment, just for the cost of 10 Gems (300 is one pull) you can reset them and get back 100% materials you used!
So here's the TL;DR for this method:
- At the start play the game normally and level the top 5 characters you actually use in combat - do this until you start hitting the level cap on them (level 80),
- Now, reset those 5 characters and instead level the 5 SR rarity ones that you have the most dupes of - getting SR is actually easy,
- Throw the characters you actually want to use in combat to the Synchro Device and they will be leveled to match the level of your top 5 character,
- Once any of your SSR get its 3rd dupe, which means you can increase the leval cap of hers to 200, do the switch again and use her as one of the top 5.
- Repeat this until you get 5 characters to level 200. Then the Synchro Device will evolve and now you will just level it instead.