Weather
The weather changes during a match, which subjects the two combatants to some handicap according to the weather, as listed below. Note that although there are weather changes in the Story Mode, they are for visual effects only and do not carry any handicap like in other modes.
Plot
Unlike previous Touhou games where the multiple endings are numbered, leading to ambiguous canonicity of each ending, Scarlet Weather Rhapsody does not number its endings and all story routes are considered as canon. This is achieved by placing all story routes in different places in the plot's continuity, though the chronological order in which the characters' stories are played out is not immediately apparent to the player.
A bizarre phenomenon is occurring in Gensokyo. In the middle of summer, untimely rain and hail fall in the Forest of Magic, snow blankets Hakugyokurou, the Scarlet Devil Mansion is enveloped in a cloudy, dense haze, and the Hakurei Shrine is levelled by a sudden earthquake. Throughout the game, Reimu and the other protagonists set out to investigate the source of the strange occurrences.
The culprit behind all these is the celestial Tenshi Hinanai. Finding her newfound life in Heaven boring and monotonous, she enviously saw the youkai of Gensokyo stirring many incidents from above. Wielding the power to control the earth and the divine Sword of Scarlet Thought (緋想の剣 Hisō no Tsurugi), the jaded celestial decides to instigate a catastrophe of her own.
Characters
Scarlet Weather Rhapsody retained all characters from Immaterial and Missing Power (except Hong Meirin) while adding three pre-existing characters of the Touhou Project into the game and introducing two new characters — bringing the total roster to 15 characters.
Reimu Hakurei (博麗霊夢) - The miko of the Hakurei Shrine, which was newly reduced to rubble. She sets out to find the one responsible for this and make her compensate for the shrine.
Marisa Kirisame (霧雨魔理沙) - A magician living in the Forest of Magic. Troubled by the rain around her, Marisa tries to go to a place where the rain won't reach her.
Sakuya Izayoi (十六夜咲夜) - The head maid of the Scarlet Devil Mansion, noticing the energy flowing out of her body, she decides to find the cause.
Youmu Konpaku (魂魄妖夢) - The gardener of Hakugyokurou. Noticing that ghosts were decreasing in number, she goes to investigate without telling her mistress Yuyuko.
Alice Margatroid (アリス・マーガトロイド) - A puppeteer magician who also lives in the Forest of Magic. Convinced that the strange occurrences are signs of an impending earthquake, she delves further in the matter.
Patchouli Knowledge (パチュリー・ノーレッジ) - The resident bookworm of the Scarlet Devil Mansion, she feels the change in the temperaments and puts the investigation upon herself since no one else seemed to realize what was happening.
Remilia Scarlet (レミリア・スカーレット) - The vampire lady of the Scarlet Devil Mansion. Remilia has to stay indoors because rain, one of vampires' weaknesses, kept falling outside the mansion. Being bored, she had her servant maid Sakuya bring in suspects of the incident one by one.
Yuyuko Saigyouji (西行寺幽々子) - The mistress of Hakugyokurou. Although she was one of the earliest to realize the change in temperaments, she did not seek to put an end to the incident but used it to further her own ends - to enjoy a cool summer.
Yukari Yakumo (八雲紫) - A youkai who looks over borders, including the one at the Hakurei Shrine. Infuriated by the Tenshi's plan to make the shrine celestial property, she seeks Tenshi out and destroys the newly-rebuilt Hakurei Shrine.
Suika Ibuki (伊吹萃香) - A party-loving oni who felt the temperaments were being gathered. Thinking the whole venture fun, she went up to Heaven to help turn Tenshi's prank into something more serious and to stay for the food and drink.
Aya Syameimaru (射命丸文) - A newspaper journalist for the tengu society of the mountain. While not searching for potential scoops, she guards the mountain from trespassers.
Reisen Udongein Inaba (鈴仙・優曇華院・イナバ) - A moon rabbit who now resides in Eientei. By the orders of her master Eirin Yagokoro, she goes around warning people for earthquakes and investigates the aftermath.
Komachi Onozuka (小野塚小町) - The shinigami in charge of bringing souls to the other side. Now just wandering around and slacking off.
Iku Nagae (永江衣玖) - An oarfish (known as "messenger of the Dragon Palace" literally in Japanese) whose task is to take notice of earthquake signs and warn the people of the inevitable disaster. Nominally under the command of the celestials.
Tenshi Hinanai (比那名居天子) - A celestial who ascended to Heaven through no virtue of her own. The tempering of the temperaments and instigating earthquakes were all her doing, due to her being bored and wanting people to "defeat" her.