Like all humans, Ashikaga Takauji ignores Elbereth. He has unimpressive base damage with two weapon attacks and an artifact-theft attack, but he will usually be wielding your quest artifact, which can potentially bisect you. This makes him one of the most dangerous quest nemeses to face in melee range, and there is no shame in considering leaving Takauji alone unless you have options to actually deal with him.
More cautious players may wait until they have a more thoroughly assembled kit with a fallback measure, usually an amulet of life saving. The samurai player monsters and ninja on the quest often carry useful attack wands, however, and it is very easy to approach the quest nemesis without disturbing him from his meditation, due to the layout of the level. The final entrance before the inner section gives you a clear shot with any ranged weapon from far enough away that he will not immediately wake up.
Ashikaga Takauji has no elemental immunities or extrinsic magic resistance, so a wand of death can kill him immediately. A wand of sleep may also work, but carries the risk of him resisting the ray and waking up to swing the Tsurugi at you.
You can also do a controlled polymorph into any large-sized or bigger monster to avoid bisection. The black dragon is the most ideal form, since using disintegration breath via the #monster command will easily kill Ashikaga Takauji without destroying the Tsurugi or the Bell of Opening.
Ashikaga Takauji is a historical figure of medieval Japan. He was Shogun from 1338 to 1358.
In SLASH'EM, the disarm technique can get Ashikaga to drop the Tsurugi with fairly decent frequency, just in case a melee fight is unavoidable. Striking will then make him teleport to the stairs and heal, leaving the Tsurugi behind.
Ashikaga Takauji was a daimyo of the Minamoto clan who
joined forces with the Go-Daigo to defeat the Hojo armies.
Later when Go-Daigo attempted to reduce the powers of the
samurai clans he rebelled against him. He defeated Go-
Daigo and established the emperor Komyo on the throne.
Go-Daigo eventually escaped and established another
government in the town of Yoshino. This period of dual
governments was known as the Nambokucho.
[ Samurai - The Story of a Warrior Tradition, by Cook ]
On July 8, 1336, he and his samurai entered Kyoto, forced Go-Daigo
to retire, after which he seized power himself and installed a
puppet prince on the throne (the current Japanese imperial family
are the descendants of this puppet emperor that Ashikaga
Go-Daigo escaped, though, wouldn't admit to have been defeated,
and opened a new "capital" in Yoshino (south of Kyoto), where he
and few of his descendants claimed to be running a government,
known as the "Southern Court". The period between 1337 and 1392,
when Japan was ruled by two courts, is known as the Nambokucho.
That "government" disappeared, naturally, after a few generations,
and Ashikaga's Muromachi regime lasted for a long time. The last
Ashikaga daimyo in power was the 14th descendant of Takauji.