無敗 is read as むはい (muhai) and means undefeated.
むはい
muhai
ぶにん
shorthandedness
むりやり
forcibly
むり
impossible
むちゃ
rash
むりょう
free (of charge)
ぶじ
good health
むしょく
without an occupation
むごん
silence (not speaking)
むせん
radio (communication)
むよう
unnecessary
むすう
innumerable
むこう
invalid