While you can obtain experience through battling various stages, there are multiple ways you can improve the various Sync Pairs you have accumulated. This is done in the "Team" section in the Pokémon Center.

Level Up

The Level Up option is a way to more increase the level of your Sync Pairs without the need to battle. To do this, you have to use Level Up manual items. You can use multiple at once so as to not have to manually keep enterring it. Each Level Up Manual has got a specific amount of Experience it boosts experience

Picture Name Boost
1 ☆ Level Up Manual+100 XP
2 ☆ Level Up Manual+1500 XP
3 ☆ Level Up Manual+5000 XP
Level Up Image

Moves & Skills

When you get a Sync Pair, they will have two moves and no Passive Skills, but using this feature you can unlock them all using various items that you find.

Unlock Requirement
Move #35 Training Machine
Move #410 Great Role Soda
3 Ultra Role Soda
30 Training Machine
5 Super Training Machine
Passive Skill10 Great Role Soda
3 Ultra Role Soda
15 Super Training Machine
10 Skill Capsule
Moves & Skills Image

Unlock Level Cap

When you first find a Sync Pair, they typically have a small Level Cap. This varies depending on the star rating of the character. Once they reach that level, they won't be able to get higher but, using items, you can unlock them even further. The standard upgrade amounts are below but various Event Sync Pairs, specifically Legendary ones, have their own requirements

3☆ 4☆ 5☆ Requirements
Lv. 50Lv. 50Lv. 608 Role Soda
Lv. 65Lv. 70Lv. 7575 Role Soda
15 Ultra Role Soda
Lv. 80Lv. 85Lv. 90150 Role Soda
75 Great Role Soda
38 Ultra Role Soda
Lv. 95Lv. 100Lv. 105450 Great Role Soda
225 Ultra Role Soda
5 Gym Leader Note
Lv. 115Lv. 120Lv. 120750 Ultra Role Soda
375 Role Soda +
15 Gym Leader Note
8 Elite Four Note
Unlock Level Cap Image

Increase Potential

Each Sync Pair is limited somewhat by their Star Rating. This means Level 3 Sync Pairs can never get beyond Level 90. However, there is a way around this. Using specific Star Power-Up items, you can boost the potential of your Sync Pair. This means that they'll get pushed up to the next star rating which increases their stats and pushes their maximum level even higher

Each item used provides a +1 to each stat except HP where it gives +2. The star level changes after 20 additions.

Increase Potential Image