At the start of each co-op game, you must make a selection to pick a character and in addition to character, a co-op role. The role determines what your game plan will be for the incoming game. Each character will have a role rating for A through E for each role, the higher the letter grade, the less points provided for deck construction. A ranks are not always guarantees that something is good, and E ranks are not always indicators of things you should never do with a character. There are lots of tricks in co-op where you have to spend time and see what some characters are still capable of.
With any role you will want to reach level 10 ASAP so that you unlock all of the point cards for the role possible and to unlock the role hyper and role ability that comes with each role. Playing single player games with fast forward will provide quick role xp, but you won't gain any xp like you would playing online. You can try single player games or spectate co-op games to see how roles work if you have no co-op experience before jumping into online games yourself. It is recommended to avoid Hyper difficulty bosses until you get to level 10 in a role.
The heavy guns, the biggest source of damage for the team in most games. Attackers are extremely important 99% of the time and every team will do well to have at least one Attacker or a situation could arise where there's no chance for survival if the game goes on too long. You will want to pick characters that do not have -1 ATK and typically a hyper that will help to boost damage or chances of fighting enemies. Picking Attacker automatically adds +1 to your REC.
After Norma buffs, Attackers will receive a +2 bonus to their ATK, so it is important to get to Norma 4 ASAP for this reason. Attackers are able to attack the boss first regardless of who engages a challenge. Sometimes an Attacker may want to stop 1 or 2 spaces ahead of a boss if they get a big enough roll to avoid an incoming boss card or to block the boss' movement for a nearby teammate in front of the Attacker since the boss will usually stop upon attacking the first player it runs into. Read the situation, teammate placements, cards the boss is about to play and any other mobs before going for a direct challenge with a boss every single time. Attacker is generally the most straight-forward role, but there are times smart plays can still be made where you can protect a teammate from getting attacked by the boss, so always be paying attention to current developments in the current match. At level 5, role hyper Ultimate Weapon in the Sun is unlocked, you can switch out your character hyper for the role hyper if you choose. The role hyper adds +3 damage to attacks that land in your next battle. At level 10, Fury is unlocked as the role ability. It is only usable in a battle but adds a +1 to damage if an attack lands. It is useful as free damage against a boss or to KO a pesky mob enemy that needs to die such as a Haruo Chicken.
Guardians, often referred to as Defenders, are one of the lesser roles in co-op, but against some bosses they are a real big help such as Jonathan or Summer Beast who have many cards that deal damage or spawn plenty of mobs. The main objective of a Guardian is to give shields/bubbles to teammates which will nullify 2 damage from the next hit a receiver takes. If the receiver rolls a high enough defend against an attack received in battle, damage can become 0. If a receiver starts a battle and ends a battle without the shield getting hit, the shield will still disappear so sometimes it is best to avoid battle panels or a direct fight to preserve the shield.
Guardians can only have 1 active bubble at a time and cost 1 HP to give to a teammate each time, so Defenders have to be mindful decide whether or not anyone is in enough danger to warrant a shield or keep to themselves from getting to 1 HP sooner. Shields cannot be given if the Defender only has 1 HP left.
After norma buffs, Guardians gain a +2 bonus to DEF so it is a good idea to get to Norma 4 asap so that it is that much harder to have a Guardian KO'd. Guardians are not expected to be dealing big damage all the time, but a character with a good hyper can still contribute at times and could be helpful such as Guardian Ellie with her character hyper. Due to Guardian being a backseat role not focused on doing big damage but keeping the team alive, role hyper might be picked more often with this role to provide the team more stacks of damage nullification to seriously slow down the team from getting KO'd. Reaching level 5 will unlock the role hyper Lifeguard on the White Beach, which provides 2 spirit defense to the whole team in each character's next battle. If a player rolls high enough alongside the spirit defense buff, damage can be nullified completely if roll + spirit beats or equals the attack roll. Reaching level 10 will unlock the Spirit role ability, which gives a +1 spirit defense to your whole team.
Supports, sometimes referred to as Healers, are often a secondary requirement to a solid team foundation. Similarly to Guardians, Supports will not always be expected to be going for lots of battles and being a big source of damage for the team as their main role is to stay alive, heal, revive, and support their team any way they possibly can with various cards or hypers. They are still able to sometimes help out in a pinch depending on their hyper, but staying alive is a priority for a Support character compared to much else except KO'ing a weakened enemy.
Any character with a positive EVD value or low REC is a good candidate for a Support character, since after norma buffs Supports will have +2 movement and +1 EVD. This extra movement will help you catch teammates to heal them or to revive them which costs (their current REC value x 3 stars). Do what you can to avoid confrontation as much as possible and don't go for any giant risks where avoidable unless there is a good chance i.e. KO'ing a weaked mob monster with a direct attack.
Since reviving a teammate can be a powerful game-saving ability, hyper choice between character hyper or role hyper can be a toss up. This choice will vary wildly by character so it is up to you to decide based on the team you see being built during deck construction. At level 5, Guardian of Blooking Flowers role hyper will unlock, which will revive a KO'd all to full health. At level 10, Restore will be unlocked as a role ability which revives a fallen teammate with 50% HP rounded up. This is typically important to revive an Attacker that has been KO'd and stuck due to high REC values or anyone else to prevent the whole team from being KO'd and losing the game. Always try your best to revive someone in a way that they won't be dying immediately afterward.
Avenger role is unlocked after reaching Attacker level 10. Avengers are an avant-garde type of damage dealer and should be considered the “bruiser” of the team. They thrive in taking a huge punch from an enemy and retaliating with a huge attack buff relative to damage taken for the battle. For every HP lost in a battle, the Avenger gains +1 ATK extra. Avengers have to play differently than attackers as they need to attack 2nd to get the benefit of their revenge attacks. Attacking first never lets an Avenger use this special revenge attack capability they have. As a result, Avengers usually want to land on boss panels as their main attack source or to land in front of an enemy to setup.
The typical character that should be picked with this role should usually have at least 5 HP and neutral ATK value, anything under these values and the value of picking Avenger begins to be lost. Negative evade values are also a better trait to have for the role so that a player can purposely fail evading a large attack roll and convert their HP into a big counterattack.
After norma buffs, Avengers will have a +2 Max HP bonus and -1 REC, which helps characters live a little longer and get back in the game sooner after a KO. At level 5, role hyper Unforgiving Avenger is unlocked, which will bring back the user to 3 HP if KO'd in battle within 3 turns of the hyper activation. Beyond is Avenger's role ability that does the same thing, but only if it occurs within 2 chapters after activation. Beyond is a huge part of playing the role, but only unlocks once you reach level 10 so you need to reach this level asap to make Avenger much more important. This is one of the most important role abilities to unlock as it is a big part of Avenger's game plan for 100% guaranteed counterattacks after surviving any attack an enemy may have thrown. Without it, Avenger is much less useful.
Dealer is unlocked after reaching Support Level 10 and can be seen as an avant-garde support role. A player with this role can send cards in their hands to teammates, but requires at least 2 cards in the Dealer's hand to use Deal and the card sent randomly chosen. The big selling point of Dealer is that the Dealer's own drawn hypers can be dealt to teammates, allowing for some potentially busted combos. Role hyper as Dealer is usually a waste since all it does is turn a hyper into a draw 2 card, leaving 1 less powerful hyper card to use.
Characters to play for Dealer wildly varies, as some have hypers that can be tremendous support for their teammates (i.e. Ellie, Suguri, Sham hypers) and others have no major benefit to passing hypers (i.e. Natsumi, Fernet, Kiriko hypers). The impact the Dealer has on damaging enemies can vary due to sending the cards that would let Dealers do the big damage to teammates or choosing to go for a play themselves, so they are the closest thing to a wild card character type.
After Norma buffs, Dealers will receive a +2 hand limit bonus and +1 HP, so is a good role to play for characters that could benefit from an extra point of HP such as Peat or Pilot Marc. At level 5, Summer Games role hyper is unlocked, which provides a stock effect of making the next panel landed on a guaranteed draw 2 cards effect. At level 10 the Demand role ability is unlocked, which does the exact same thing as the role hyper contained as a role ability. This is an important tool to open with in games and a form of protection in the later game so should be used more wisely the longer the game goes on.