Jinwoo's poison immunity means he can turn Akame into a Shadow. Shadow Akame with Muramasa would be a powerful asset, especially against S-Rank Hunters.
If Jinwoo avoids Lightning Blade, he can defeat Kakashi, especially with Igris and Iron. Shadow Kakashi's versatility (ranged ninjutsu and close combat) would be a huge asset, and his Lightning Blade could even pierce Solo Leveling armor.
Shadow Gyomei's Stone Breathing (flail and axe) can quickly clear lower-level threats, though he might struggle against S-Rank and Monarchs. He's good backup for Jinwoo.
Shadow Itadori, especially with Domain Expansion, could likely solo a Monarch. His Black Flash technique would devastate even heavily armored high-ranking Hunters and most Dungeon Bosses.
Shadow Edward's Alchemy provides great support, from battlefield manipulation and impaling enemies to creating protective domes. His Alchemy skill is crucial for his usefulness.
Shadow Yamcha's attacks can devastate Hunters and armor. His Ki blasts, especially the Kamehameha, pose a serious threat even to Monarchs, leaving them open to Jinwoo.
Shadow Ichigo's Getsuga Tensho and Jūjishō attacks are devastating. His Bankai form offers superhuman speed, and his Blut Vene could make him a useful tank.
Shadow Uvogin makes a great berserker and tank, charging into Dungeons and clearing them. His Big Bang Impact punches can devastate even S-Rank Hunters and Bosses.
Shadow All Might's United States of Smash could defeat most Solo Leveling bosses. His strength and speed make him a great offensive asset, but his durability also makes him a valuable tank.
Jinwoo's Shadow Extraction ability allows him to turn powerful characters into loyal Shadows. While requiring a kill, these Shadows retain their superhuman abilities, becoming valuable assets against Monarchs, monsters, and Hunters. Some are even strong enough to solo S-Rank threats. Their regeneration, fueled by Jinwoo's mana, ensures their continued service.