Having convinced Ymir Fritz to aid him, Eren Yaeger (Attack on Titan) unlocked the full power of the Founding Titan, becoming the most powerful Titan in history alongside Ymir Fritz herself.
Baryon Mode (Boruto: Naruto Next Generation) is a form that allows Naruto to acess the highest level of Kurama's power different from Kurama and Six-Path Sage Mode allowing him to dominate opponents neither form could allow him to at the cost of Kurama's eventual death.
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, he gained full mastery of all aspects of his power and reached entirely new heights, evidenced by a fully stable Partial Transformation
Through the X-Antibody (Digimon) a Digimon can evolve to draw out their maximum potential and reach their species' full level of power.
During his battle with Jiren, Goku (Dragon Ball series) was able to assume his most powerful state of being and completely master Ultra Instinct.
After his revival and months of 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)
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, for one minute per day, Escanor (Seven Deadly Sins) becomes The One, an invincible, godlike warrior...
...And upon burning up all his lifespan, he becomes "The Ultimate One" for the remaining life he has.
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.
By combining the power of Archdemon Lucifer and the Vanishing Dragon, Vali Lucifer (Highschool DxD) evolved his Balance Breaker into Diabolos Dragon Lucifer, granting him absolute power surpassing the Heavenly Dragon.