In Genshin Impact, constellation 6 can significantly boost characters' power and support capabilities.
When it comes to Genshin Impact, players not only want to own characters but also aim to have enough constellations to optimize their abilities. A character can have a maximum of 6 constellations, and those with all constellations are often referred to as C6.

An interesting fact is that these characters can become extremely strong and useful after reaching C6. Not only 5-star characters, but many 4-star characters also need to reach all constellations to optimize skills and damage. Below are some C6 characters that players consider most worth owning in Genshin Impact.
1. Hu Tao
C1: When activating elemental skill, Hu Tao's Pyro damage attacks do not consume stamina.
C2: Damage of Blood Blossom on enemies increases by 10% based on Hu Tao's HP. Hu Tao's elemental skill can trigger this effect.
C4: After defeating an enemy marked by Blood Blossom, characters (excluding Hu Tao) in the party will increase crit rate by 12% for 5s.

C6: When Hu Tao's HP drops below 25% or she is about to die, Hu Tao will not immediately collapse, but in the next 10s, her physical and elemental resistance will increase by 200%, crit rate increases by 100%, this skill has a 60s cooldown.
Hu Tao's C1 is the most desired constellation for many players, as it is easier to obtain than the remaining constellations and is useful in combat. The other constellations mentioned above are also extremely useful for a DPS like Hu Tao and can even support other players. At C6, Hu Tao is almost immortal for 10s, albeit brief but enough to turn the tide thanks to her extremely powerful nuking ability and self-healing.
2. Xiao
C1: Increase the number of uses of elemental skill (E) by one.
C6: After using the elemental burst, hitting at least 2 enemies with an attack, E immediately gains an extra usage, and within the next 1s can bypass the CD of skill E.

Xiao's other constellations are not noteworthy or necessary. However, Xiao's 6th constellation has propelled this character to new heights. Players can continuously utilize Xiao's elemental skill, inflicting significant and continuous damage.
3. Zhongli
C2: Elemental burst can create a shield for oneself and other players
C4: Increase elemental burst damage by 20%, extend the frozen effect of enemies by 2s.
C6: When the Jade Shield takes damage, 40% of that damage will be converted into HP for the character. The amount of HP restored cannot exceed 8% of the character's HP.

As a support character specializing in shielding and nuking, Zhongli proves most useful in co-op at C2, providing shields for other players. Zhongli's C4 and C6 constellations are also highly desirable, enabling this character to both support and deal damage while healing HP.
4. Raiden Shogun
C1: Wishes accumulate Energy faster. Electro characters, after unleashing their Burst skill, will accumulate Energy by 80%, while characters of other elements will gain 20%.
C2: After unleashing the Elemental Burst, Raiden's attacks will bypass 60% of the enemy's defense.
C4: When the Elemental Skill ends, team members (excluding Raiden) receive a 30% attack increase for 10s.
C6: In the Transcendence state of the Supreme Soaring Thunder, Raiden Shogun's Elemental Burst damage hitting enemies will reduce the Elemental Burst CD by 1s for all characters on the team (excluding Raiden).

Raiden Shogun has become a favorite character for many players, not only dealing massive damage but also possessing extremely good support capabilities. Especially with constellations 4 and 6, Raiden's support abilities as well as her damage have been elevated to new heights.
5. Kazuha
C1: E skill CD reduced by 10%, using the Elemental Burst will reset E's CD.
C2: After using the Elemental Burst, the 'Burst of the Breeze' area will help characters within it increase their elemental mastery by 200.
C4: When Kazuha's elemental energy is below 45, increase elemental energy points when using E skill.
C6: Within 5s after using E or Q, Kazuha will infuse with the Anemo element, while each point of elemental mastery increases normal attack damage by 0.2%.

Kazuha is regarded as the best support character in Genshin Impact at the current time, for many different reasons. At C0, Kazuha can provide good support or sub DPS, but with C6, Kazuha can excel even further in that role, even becoming a DPS.