User is able to ascend/evolve/transcend their condition, powers and abilities to the highest level allowing them to obtain unparalleled might, becoming an unstoppable force. The user also gains access to the ultimate level of power that is capable of transcending the boundaries of their own species. Most importantly, zenith can be obtained by those who possess full mastery of their own powers or ones with the utmost potential.
In the Avatar State, Avatars such as Aang (Avatar: The Last Airbender/The Legend of Korra) are at their most powerful, enabling them to channel vast cosmic energies and the knowledge and spirits of all past Avatars.
In his Ultimate form, Ben 10,000 (Ben 10: Ultimate Alien) can instantly use any of his alien powers without changing form...
... , as well as access Anodite magic.
Kal Kent (DC Comics), an evolved Kryptonian from the year 1 million, possesses vastly evolved Kryptonian powers, as well as several others as a result of additional alien, extradimensional, and supernatural admixtures in his bloodline.
White Raven (Teen Titans) is Raven's most primal, significant, and powerful form, mostly shown as a symbol of her highest hidden power and her inner purity against the consuming evil of her father Trigon.
Jean Grey (Marvel Comics) as the White Phoenix of the Crown.
Cornelia Hale (W.I.T.C.H) at full Zenith becoming one with her dragon
Irma Lair (W.I.T.C.H) at full zentih
Guardians of the Veil W.I.T.C.H (W.I.T.C.H.) after becoming one with their elemental dragons.
Sōsuke Aizen (Bleach) gained godlike power upon becoming one with the Hōgyoku, with his final form transcending the limits of Soul Reapers and Hollows alike.
When using the Final Getsuga Tensho, Ichigo Kurosaki (Bleach) fuses with Zangetsu and his inner Hollow, reaching his highest state of power, at the cost of burning through them.
After discovering his true nature and potential, Ichigo Kurosaki (Bleach) gained full mastery of all aspects of his power and reached entirely new heights, evidenced by a fully stable Partial Transformation.
During his battle with Jiren, Goku (Dragon Ball series) was able to assume his most powerful state of being and completely master Ultra Instinct.
Vegeta's (Dragon Ball series) desire to defeat Jiren and revive Universe 6, caused him to push himself through all his limits out of sheer willpower, and achieve his ultimate state of power, Super Saiyan Blue Evolved.
After revival and intense training, Frieza (Dragon Ball series) achieves the strongest transformation of his race, the Golden Form. After intense training and discipline while in Hell, he gained perfect energy manipulation, becoming True Golden Frieza.
Jiren (Dragon Ball Super), after being overpowered by Ultra Instinc Goku, refuses to lose and pushes himself past his limits.
Gon Freecss (Hunter X Hunter)
After receiving the chakra of all nine Tailed Beasts, as well as half of the power of the Sage of the Six Paths, Naruto Uzumaki (Naruto) reached his highest state of power, Six Paths Sage Mode.
Saitama (One-Punch Man), after breaking his physical limits, has shown immense strength that has remained unparalleled by anyone.
Pegasus Seyia (Saint Seyia) is wearing a God Cloth, a Bronze Cloth reborn from Athena's blood, and above nearly all other Cloth types, inferior only to the Kamuis of the Olympian Gods.
After eating the final phantom ingredient, CENTER, Acacia (Toriko) achieved his ultimate form which would allow him to consume NEO and become unstoppable.
Astraea (Sora no Otoshimono) evolved to her absolute peak state after activating her Pandora System twice.
Evangeline (UQ Holder) has evolved past her original state of power after 80 extra years of being alive, allowing her to master Magia Erebea to a whole new level, granting her the power of Krystalline Basilea a state beyond Queen of Ice.
Medaka Kurokami (Medaka Box) has reached her highest state of power, End God Mode.
After combining the power of the Welsh Dragon and the Ouroboros Dragon, Issei Hyodou (Highschool DxD) evolved his Balance Breaker into its Diabolos Dragon form, granting him absolute power that far surpasses even the Heavenly Dragons.
Galand (Seven Deadly Sins) when he activates his ability Critical Over augments his physical power to it's absolute limits until his magic power runs out.
At high noon, Escanor (Seven Deadly Sins) becomes The One, an invincible, godlike warrior.
After receiving energy from all of the Spirits, Tohka (Date A Live: Mayuri Judgement) achieves her ultimate form, Full-Form Astral Dress: Twin Blades Mode.