Directly before challenging
Leon to become the next
Galar Region Champion,
Chairman Rose will awaken
Eternatus in order to recreate the Darkest Day. Leon will rush off in hopes of stopping Eternatus, and
Hop will suggest heading to the
Slumbering Weald to get the help of
Zacian and
Zamazenta to also do so. However, at the end of Slumbering Weald, you actually won't be able to enlist their help. Instead, you and Hop will discover the
Rusted Sword and Rusted Shield. The two of you will take them, believing they might be able to assist Leon enough to help all of you defeat Eternatus. If you have
Pokemon Shield, your player will hold onto to the Rusted Shield and Hop will keep the Rusted Shield.
From there, your trainer will keep the Rusted Shield for the rest of their journey. Both items will help you and
Hop summon
Zacian and
Zamazenta to help defeat
Eternatus on top of the summit of the Energy Plant. Later on during the
Post Game, you will have to protect the Rusted Shield from
Sordward and
Shielbert, eventually giving the Rusted Shield to Zamazenta before going into battle with it.