second
bottleholder
contester
monomachist
coparticipant
contender
hold the ring
agonist
go to bat
encounterer
participant
assertor
competitor
coquetter
combater
Hellanodic
Law of Conservation of Ninjutsu
gamesman
opponent
gunfight
play
take on
agonistarch
alliancer
meet
swordplayer
encounter
compete
coopetitor
competitorship
mano a mano
outduel
presentation
old stager
dueling
duel
champion
stager
old-timer
battle it out
oldtimer
adjunct
warhorse
veteran
old hand
adversary
challenger
fighter
logroller
coruler
interactant
racketeer
overleveled
forefighter
swordfight
interactor
dueler
duelist
duellist
sport
dueller
event
oppugner
batman
stickler
sidekick
measure swords with someone
maintain
counterpetitioner
uphold
second fiddle
foiler
cowinner
shield
game
concurrent
gamesplayer
gomer
gameplayer
power gamer
over-the-board
with friends like these who needs enemies
handler
kiss-ass
tilter
tie
vice
matched
counterplayer
cross swords
ruck
objurgator
den mother
kemper
aide
to find a better fitting word. Finally, thanks to ChatGPT, the overall results have been greatly improved.