Tropes for "The Red Mist Incident, Part 3" include:
Adaptational Wimp: In the games, Flandre was the Stronger Sibling of the Scarlet Sisters. Here, she struggles to just keep up against Remilia and, while Remilia ends the fight with a hug, the older sister was clearly the victor by that point. Though it is shown at the end that she's much stronger in the present, the Trope still applies since she's shown to be merely fighting her sister on equal terms.
Aw, Look! They Really Do Love Each Other: Remilia and Flandre in the second half of the episode. They challenge the heroines hand-in-hand, and after Reimu defeats them, they are found lying unconscious, hand-in-hand once again, with peaceful smiles on their faces.
Beam-O-War: No less than two instances. First, Remilia's Gungnir versus Flandre's Laevateinn, then Remilia's Gungnir versus Marisa's Master Spark.
Brick Joke: Nitori, who was kicked out of the shrine in Part 1, is seen in The Stinger of this episode stumbling upon Shou and Nazrin preparing to unseal Byakuren.
Cooldown Hug: Remilia gives Flandre one to stop Flandre's rebellion against her.
The Glorious War of Sisterly Rivalry: Sakuya is moved to tears that Remilia and Flandre having fights with each other is such a big improvement over their previous relationship.
Let's You and Him Fight: After finding out that Marisa basically provoked Flandre to attack Remilia, Reimu is only too happy to let Flandre take care of the incident by herself. Unfortunately, Remilia quickly pacifies Flandre, and the ensuing fight becomes a two-on-two battle.
Nice Job Breaking It, Hero: Marisa successfully incites Flandre to rebel against Remilia. After a short scuffle, however, Remilia embraces Flandre and apologizes for everything she did, mending their relationship, and adding a powerful adversary.
Theme Tune Extended: The opening theme for this episode is the second half of the piece used as the opening theme of "The Red Mist Incident Part 2".
There Is No Kill Like Overkill: Reimu ends the battle against the Scarlet sisters with a giant Yin Yang Orb several times the size of the Scarlet Devil Mansion.
Used to Be a Sweet Kid: Flandre, but 495 years of being ignored has caused her to act out. She gets better.
We Can Rule Together: Remilia attempts to subdue Flandre's rebellion against her with this.It works, because Flan only wanted to go outside in the first place, and that was Remilia's goal at the outset.
