The Aoi family's names all mean different things. The family name, Aoi, is the Japanese word for the flower hollyhock. Shuu's name means "holly" but it's a homonym with the word for "the end". His mother's name, Saki, means "to bloom". And Shuu's father is named Ren, which means "to connect".
Fifteen has the kanji for fifteen on his helmet.
Tsukasa eats a parfait shaped like Decade's mask.
Jin tells Takumi to look towards the sea. Probably because X has a sea theme. The food they eat also looks like seafood.
Takumi befriends Jin and Mari. Mari has the same name as the main heroine of Faiz.
There's several references to Takumi's nekojita sensitivity to heat, which was a trait of his during Faiz.
Futo's mascot can be seen when Tsukasa is talking with Shoutarou.
Shuu's message "Hate you" (Ki-ra-i da きらいだ) when flipped around is one character away from being "Love you" (Da-i su-ki だいすき).
This movie features a lot of numbered Riders. Decade (10), Faiz (555), Gaim (Heisei Rider 15), W (2), Kaixa (913), Ichigou (1), X (10), ZX (Showa 10th anniversary Rider), Fifteen (15).
At the end, the movie has two dedications in English. The first is to Hirayama Tohru, a producer for Showa Kamen Rider TV series who passed away in 2013.
The second dedication is to Nagaishi Takao, who was a director for Heisei Riders from Kuuga to Decade. Nagaishi also passed away in 2013. His last Rider directing credit was Decade 29.
According to the Japanese wiki, there are several stunt actors who make unmasked cameos in this movie. The two workers at the beginning who are killed by Badan are Takaiwa Seiji (Mr. Heisei Rider) and Niibori Kazuo (he was the stunt actor who guested on AkibaRanger).
On the black placard at the little shrine his parents have for Shuu, is written his Buddhist name. A Buddhist name is given to a person who's died so that they don't come back if their name is called (Ironic since he comes back anyway). While it's not clear the the pronunciation is, his Buddhist name is 葵柊光童子位 which would translate to "Aoi Shuu a child of light". [1]
Continuity
Mitsuzane calls Zangetsu Shin Niisan in battle, but maybe no one heard.
If this movie is canon, then Inui Takumi survived the events of Faiz and spent the last ten years working at a laundrymat called Kikuchi. It also acts as an epilogue to the series, since Takumi is still dealing with the traumatic events from that series.
Takumi and Jin meet a restaurant called Yoshidaya. Not sure if it has any connection to Faiz or X.
Blu-ray Collector's Pack
DVD
DVD Collector's Pack
