Each bot has a Tier, Rank, and Level. You can see this information by going to your BOTS tab on your home screen, then tapping on your bot, and opening the INFO panel.
Tiers range from 1-star to 4-stars, and cannot be changed. The higher the tier, the better the stats of your bot. Tiers control synergy bonuses and allow your bot to rank up higher.
Levels and Ranks can be increased.
Levels increase the power of a bot. Ranks increase the max level of a bot. For example, your bot can reach level 10 in rank 1, and level 20 in rank 2. The level cap is always 10 times as much as the rank.
When your bot reaches the maximum level for the rank, you will be required to rank up in order to unlock new levels. Ranking up will also increase the effectiveness of normal abilities like Bleed, Armor Break, etc.
Maximum Rank for Each Tier:
1 Star: Rank 2
2 Star: Rank 3
3 Star: Rank 4
4 Star: Rank 4
Maximum Levels for Each Rank:
Rank 1: 10 (1 to 4 Stars)
Rank 2: 20 (1 to 4 Stars)
Rank 3: 30 (2 to 4 Stars)
Rank 4: 40 (3 to 4 Stars)
Remember that you will need to rank up 2-Star and 3-Star Bots to unlock their tier 2 and tier 3 specials (respectively).
1-Star Bot: Starts with a one-bar special attack
2-Star Bot: Starts with a one-bar special attack
3-Star Bot: Starts with a two-bar special attack
4-Star Bot: Starts with a three-bar special attack