Showdown is a quest in Chapter 12, "Fight for Survival", in Final Fantasy VII Remake, taking place in the pillar at the Sector 7 Slums. Cloud Strife and Tifa Lockhart fight through the Sector 7 Plate to prevent it falling.
After the cutscene ends, run upstairs, and a vending machine and bench can be found. Use the bench to heal, then head up the final set of stairs commencing a cutscene. During this, hold for the Menu to select materia for Barret, who joins the party for the next boss. Ensure that all characters have Healing Materia (Cloud can pair it with Magnify Materia to heal all party members), and someone should also equip Cleansing Materia, and Barrier Materia can also be helpful. Elemental Materia is unnecessary for this battle, and can be removed. Most damaging Magic Materia, is weaker in this battle than others, though Wind Materia is the best option. Finally, upgrade all characters' weapons as high as possible before beginning the battle. Barret should equip the Light Machine Gun in order to use Lifesaver, if not already learned.
After the cutscene, a boss battle commences against Reno. Reno attacks quickly, and is capable of knocking one character up in the air, though this gives the others an opportunity to pile on Reno with attacks. Barret can absorb a lot of this damage with Lifesaver, meaning the party will only have to focus on healing him. After he has finished moving, Reno will be temporarily stationary, providing a great opportunity for Cloud to use abilities, Tifa to use her Unbridled Strength, and Barret to use Overcharge.
After Reno loses a third of his HP, a bombing run takes place; run to avoid it, or guard to reduce as much damage as possible, then heal. Reno will now use similar attacks as before, though he can also use Pyramid to trap a character; pressure Reno to end this. After taking damage, Reno will exit the fight temporarily, and Rude will fly in with a helicopter; use Barret to shoot at it and cast spells against it, causing it to crash.
After this, Rude and Reno are both fought. The tactics against Reno are the same as before; avoid his attacks, and then use physical abilities to deal most damage. Rude is similar, though Rude can also occasionally block damage. He can seize characters, disabling them temporarily, and his attacks can stun if not avoided. While Rude focuses on one character, use the abilities of another. Barret can use Lifesaver to take most of the damage, and Barrier can be cast on a character to make them resist Rude's damage. Barret should also stay at a distance and shoot as Tifa and Cloud engage the two in close combat. Defeat Reno first before targeting Rude second to complete the battle.
Once the battle ends, a cutscene commences. After this, run around the fallen plates to catch up with Tifa, leading to a final cutscene, after which the next chapter, "A Broken World", commences, with the quest "Through the Rubble".
Hard mode tips
As before, healing and barrier materia are useful, and it is ideal to pair one or the other with magnify materia to cast Manaward on all. For this battle, Time Materia and Binding Materia are crucial on different characters to cast Sleep and Stop respectively. Parry Materia is excellent on both Cloud and Tifa. Offensive spellcasting is mostly unimportant for this fight.
Cast Regen as the fight begins, and use Barret's Lifesaver and Steelskin. For the first phase, Cloud's Counterstance is helpful, though the best route is to wait for Reno to attack and then switch party member. For instance, while Reno focuses on Cloud, Tifa can use Omnistrike or Barret can use Overcharge or Maximum Fury to deal heavy damage to Reno. For the second phase, the strategy is similar; use Barret to destroy the helicopter, while Cloud and Tifa use physical attacks. Prioritize destroying the pyramid when Reno uses it.
When both Rude and Reno appear, it is possible to cast Stop and Sleep interchangeably. If one is cast and applies successfully, they become vulnerable to attacks. Lay into them with attacks, then cast the other straight after and continue attacking. Otherwise, the same strategy applies; simply allow them to focus one character, and attack with another. Casting Barrier can also be helpful, though Barret's Lifesaver should normally be sufficient.
Defeating Rude and Reno rewards Barret the Sharpshooter's Companion Vol. VII.