Chapter 7 of Beast of Reincarnation, titled "Root Rot," begins in the Ooi Colony within the Giant Tree Zone. Following an encounter with the Nue Malefact, players must guide Emma and Koo to investigate the source of recent attacks by two flying Nushi.
Navigating the Giant Tree Zone
Your initial objective is to head towards the Giant Tree to locate the two fleeing Nushi. Upon exiting the Cleanse Walker, proceed towards the Colony. To the left, climb the rusted pipes to find a Keeper Golem who can mark a Swordmaster Golem on your map. Return to ground level and take the first left to enter the Ooi Colony building. Inside, ascend the spiral staircase to find a Maneki-neko decorative item. Exit the building and continue towards your objective, which will lead to a large ruined building. Use the elevator platform in front of you to descend.
At the bottom, locate the glowing orange butterflies and climb the containers to reach a yellow cable car. Ride the cable car until it reverses direction; a platform below will hold a strongbox containing the Amber Breastplate armor. Nearby, you can find the Giant Tree: Root Depths Campsite. Rest here before proceeding.
Continue towards your objective, engaging any flying malefact enemies. Head right and climb a tree branch. To your right, grapple to a steel tower. Opposite it, you'll find more flying malefacts and a Strongbox. This Strongbox requires a directional input puzzle to open, with the solution being Right, Down, Up, Left, Up. Inside, you'll find loot for Emma, Koo, and the Cleanse Walker, along with Ancient Books.
Return to the tree roots above and continue towards your objective, clearing out Golems and bear malefacts. You will eventually reach the Giant Tree: Bulkhead Entrance Campsite, where an Ancient Golem and Control Panel are located. Interacting with the Control Panel reveals it is inoperable without a key, changing your objective.
Finding the Giant Tree Key
The Ancient Golem advises that a Golem near the red smoke holds the necessary key. Instead of proceeding towards the smoke via cable cars, explore the steel platforms around the Ancient Golem to find an elevator. This elevator leads to a ruined tower area. Ascend this tower using cable cars and Emma's hair. Inside, unlock the Ruined Tower Interior Campsite. On the floor above, you must defeat an Elite Enemy Golem, which drops the Giant Tree Key and the Fall Thunder sword. Before leaving the area, descend the tower's stairs to find the first Dragon Vein Shrine for this chapter.
Opening the Bulkhead and Progressing on Line 0
Return to the Giant Tree: Bulkhead Entrance Campsite. With the Giant Tree Key, interact with the Control Panel to open the bulkhead door. Proceed to the Cableway - Line 1: Base Station Campsite. Speak to the Ancient Golem to the right, who provides Card Key (Line Zero) and directs you to a cable car, though he notes it requires a specific key he cannot provide.
Enter the cave behind the Ancient Golem to find the key. Inside, defeat a Wolf Elite Enemy to obtain the Skill Amber: Amber Crush. Continue past this area, dealing with Golems and bear malefacts, but do not immediately head to the cable car objective. Instead, stay on the ground level and go past the steel scaffolding to reach the Cableway - Line 0: Base Station Campsite. Further north, past the campsite, find another cable car atop scaffolding. Ascend the stairs to find a Curious Golem.
The Curious Golem explains that malefacts have stolen an item from him, promising a reward upon its return. After this conversation, return to the Line 0 cable car and use your Card Key to activate the ropeway. Upon arrival, head left along the steel scaffolding towards the Giant Tree: Feeding Grounds Campsite. Here, you will find a Merchant Golem with new Skill Ambers in stock and the second Dragon Vein Shrine for this chapter.
Defeating Corvus
Past the Merchant Golem lies the boss arena for Corvus, a large flying crow-like malefact. Defeat Corvus using elemental arrows and Koo's Bloom Arts to stagger it, then use Blade Arts. Utilize grapple points to avoid projectile attacks and corrosive pools, and collect arrows scattered around the arena. Upon defeating Corvus, you will receive Nushi Skill: Acid Burst Nobudou, the Nobudou: Burst Bloom Art, and Blade Art: Nobudou. You will also acquire Card Key (Line One) and a Light Box.
The Second Nushi Encounter
Rest at a Campsite if necessary and return to the Curious Golem near the Cableway - Line 0: Base Station Campsite. Hand over the Light Box to him. If you claim you did not look inside, he will reward you with the First Moon sword. 
Proceed to the cable car beside the Curious Golem to find the Corvus Malefact Statue and additional loot. Return to the Cableway - Line 1: Base Station and enter the white cable car to reach the Giant Tree: Lair Entrance Campsite. This area features another Merchant Golem and the second Nushi fight.
This encounter with Corvus is similar to the first, but the boss now has a second phase and summons smaller corvid malefacts. Exploit Corvus's lightning weakness and attack aggressively when staggered to prevent it from summoning reinforcements. Defeating Corvus a second time will allow you to proceed deeper into the Giant Tree. Follow the path to find the Doctor S's Report document, triggering a cutscene. Return to the Nushi's lair for another cutscene.
Upon returning to the Cleanse Walker, you will be rewarded with Corvine Memories, which unlocks the Nobudou: Burst 2 Bloom Art and Finisher: Nobudou, concluding Chapter 7. The next chapter will take place in the Crater Zone.