Asura Cryin'[from anime with same name] - if my memory serves right, it can warp the fabric of time/space
From Occult Academy - "the key"
Spoiler:
which is the main character, once again if memory serves right
can warp time & space.
Shaman King - the badguy, Haku if I remember right, although only boasted about recreating Earth, think he can do more than that
To Love Ru - One of Lala's inventions certainly has to be overpowered shit that never got any airtime.
Zombie Loan[manga] - the "observers" can do pretty much what the hell they want, they never get their asses up to do it.
Folka Albark and his Shinka Ialdalbaoth...I don't know how to say it...just watch the vid...
Ialdabaoth Apotheosized is awesome, but in the end its just a mecha sized Kenshiro, it would probably be a High tier 4.
Also, Yoh did not kill Hao at the end of Shaman King, even when the whole party had elemental spirits and were pretty awesome, Hao still killed them all many times before
Spoiler:
his mother arrived and convinced him to stop fighting
I think Kakeru from Psycho Buster can be considered overpowered because his ability lets him manipulate time as well as giving him luck that would make Kyousuke Nanbu jealous... which means he can Za Warudo, revive the dead, be killed and come back to life... basically there is no way to kill him.
Also, Yoh did not kill Hao at the end of Shaman King, even when the whole party had elemental spirits and were pretty awesome, Hao still killed them all many times before
Spoiler:
his mother arrived and convinced him to stop fighting
LOL, you're talking about the KAnzenban version right?
That's simple. The public, They're the reason why the manga/anime universes exist. Without them, the authors wouldn't do anything. :P
Now seriously speaking, Mar-Vel or Genis-vel or whatever (the guys from marvel comics that were featured as the Marvel main superhero). I remember that there was one character whose name ended in -vel that not only could bend time/space and reality but actually did it.
It is not enough to have the capabilities, the character has to do it to be proven