.In Wuthering Waves, players can capture and equip "echoes" - manifestations of creatures and enemies you can find in the open world that you can equip to improve your character's stats, apply bonus effects through the Sonata effect, and even assist them in combat. In this guide, we will briefly cover the game's Echo system.
Echoes have the similar function as artifacts in Genshin Impact or Relics in Honkai Star Rail. Each character can equip up to five echoes although the actual number of echoes a character can equip will depend on the player's current Cost limit and the total cost of equipping these echoes. Individual echo costs can be 4, 3, or 1. We will cover the game's Echo Cost system in a separate guide for brevity.
Absorbing echoes is an integral part of the game as you can absorb normal non-human enemies that you encounter as well as the overlord-class bosses and certain calamity (weekly) bosses. After defeating an enemy, they'll leave a transparent silhouette. Just get close enough and press the displayed Absorb button to absorb the echo. The chances of an echo dropping its absorbable silhouette depends on your Base Drop and Enhance Drop rates, both of which are tied directly to your Data Bank level. Basically, the higher your Data Bank level gets, these drop rates will increase as well.

At Data Bank LV 8, you'll start getting the chance to absorb 4-star echoes and once you reach Data Bank LV 10, you'll be able to absorb 5-star echoes. Once you reach Data Bank LV 21, all echoes that you can absorb will be guaranteed 5-star ones.
For more information about the Data Bank system of the game, please refer to our dedicated page about this feature.
As mentioned above, each character can have up to 5 echoes equipped. There's no restriction on what type of echoes you can equip on your characters but for efficiency, it's recommended to give them echoes that will activate beneficial Sonata Effects that will go well with their skill set and role in the party.

The echo on the first slot allows the character to activate the echo's Echo Skill in combat. Usually, you'll want the 4-cost echoes here with skills that complement the equipping character's element. For example, Thundering Mephis' echo skill deals electro damage while also increasing the current character's Electro DMG and Resonance Liberation DMG so it is ideal for Electro DPS units like Calcharo or Yinlin.
Equipping Echoes with the same type (Sonata) will activate Sonata Effects. Equipping 2 same-type echoes or a full set of 5 echoes of the same type will activate the Sonata Effects for the set. When you have a full set equipped, both the 2-piece and 5-piece effects become active. Full Set Effects are usually more potent but it is also possible to mix and match different effects by equipping 2-piece and 3-piece Echoes of the same type as needed.

Do remember that copies of the same echo don't count towards the activation of Sonata Effects. If you don't have enough echoes of the same type, you can still equip identical copies as placeholders and for stat boosts, especially in the early game. Phantom Echoes (shiny echoes) are not counted as well since they are just practically skins for your echoes.
For the complete list of Sonata Effects, please refer to our dedicated page about the topic.
The number of echoes you can equip per character will depend on your Cost Limit. This cost limit is an account-tied value that's dictated by your Data Bank level. You'll start off with a cost limit of 8 and you can reach the maximum cost limit of 12 after reaching Data Bank LV 9. To be able to maximize all echo slots, you can do the 4-4-1-1-1 (total cost: 11) or the 4-3-3-1-1 (total cost: 12) combinations. Whatever combination you use, as long as you take advantage of the Sonata Effects and setting an ideal primary echo (1st slot) for the current character that matches their element and ability, you'll be able to effectively utilize the echoes' effects and stat boosts.

Echoes can be leveled up and tuned. Increasing their levels will improve their stats and for every five levels, you'll be able to Tune them to insert a random substat. Your echoes' rarity will determine their max level. You can only tune 3-star echoes and above; so this means 3-star echoes can only get 3 substats after tuning at max level, 4-star echoes get four, and 5-star echoes can have up to 5 random substats.

The materials needed for upgrading and tuning your echoes can be farmed from Tacet Field Suppression Challenges. As long as you have enough materials, you can conveniently max out the level of an echo and apply all Tuning attempts at the push of a button.
For more information about upgrading your echoes, kindly consult our dedicated page for it.
Data Merging allows you to combine several echoes to create a new one. The created echo is random and its rarity will depend on your Data Bank level as well. This feature gets unlocked at Data Bank LV 8 but I strongly suggest to avoid using this feature frequently until you at least reach Data Bank LV 15. DB Level 15 unlocks the probability to get a 5-star echo through normal means and Data Merging, included.

Just continue absorbing echoes and completing Tacet Suppression Challenges to stock up on normal echoes then use them all once you have access to Data Bank LV15. Take note that you can only get echoes that you have already absorbed before so you can't use this feature to get new, undiscovered echoes. You can't also get 5-star versions of boss echoes in this option so you have no choice but to keep fighting them over and over for a chance to get their 5-star echo drop.
We have questions and answers related to this topic which may also help you: