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.
Quon Miduchi (Towa no Quon); via Complete Transformation
Issei Hyodou (Highschool DxD); via Diabolos Dragon
Vali Lucifer (Highschool DxD); via Diabolos Dragon Lucifer
Dante (Devil May Cry); via Majin Form
Ultimate/God Rugal (Capcom vs. SNK 2)
Mega Man X (Mega Man X); via Ultimate Armor
Nightmare/Night Terror (Soul Calibur)
Asura (Asura's Wrath); via being powered by the Mantra Reactor.
Kratos (God Of War)
Sora (Kingdom Hearts); via Final Form
Wise Oracle (Valkyrie Crusade)
Ultra-Miximum Max (Mixels) via Rainbow Cubit
Godzilla (Godzilla: Final Wars); via Kaiser powered by Ozaki
Hayato Furinji (HDSK)
Duke "G" man (Ryan Tomlinson)
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.
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 thier elemental dragons at thier full Zenith
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.
During his battle with Jiren, Goku was able to completely master the Ultra Instinct form and assume his most powerful state of being, Instinct Complete.
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・Shinka.
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.
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 (Nanatsu no Taizai) when he activates his ability Critical Over augments his physical power to it's absolute limits until his magic power runs out.
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.