NOTE: This Wild Mass Guessing contains Epileptic Trees that may spoil the intense storyline of Shinkenger. Visit this particular grove at your own risk!
The Shinkengers are all related to a greater or lesser extentNone of the current batch are closely related; but, given that their families have been working together in close proximity for 18 generations, it would defy human nature if there weren't any romantic entanglements among or within the various teams. Genta being the first ShinkenGold is the exception. Takeru might not be if it turns out he's from some Branch House of the Shiba Clan
Genta, DaiGoYoh, the Ebi Origami and Ushi Origami will be critical in defeating Doukoku once and for allNone of the previous generations had a Sixth Ranger. Genta was the one who created the Ebi Origami and DaiGoYoh, and so they've never been involved in the climactic battles before. The Ushi Origami (and its combinations) are older, but they've been sealed the entire time, so this applies to them, too. Semi-confirmed and Semi-jossed.
The Nanashi can evolve into Ayakashi like the Rinshi turning into Rinrinshi from GekirangerThe Gedoshu are the basis of the various obake and youkai that crop up in Japanese legends. But if they've been pruned back by 18 generations of Shinkengers, then either the current batch have been powerful enough to survive to create legends or they have some way of replenishing their numbers. Assuming the second option: a defeated Ayakashi's spirit returns to the Sanzu River and possesses a Nanashi and eventually restores themself, but this takes a long time. So the gap between attacks are caused by the Gedoushuu waiting for enough Nanashi to turn into Ayakashi.
The cost of the BattleWhile there is no show Canon or Word of God to this effect, fan speculation that all the current Samurai-tachi's parents served under the prior Shinken Red leads to some interesting thoughts. Besides Takeru's father dying, the flashback in episode 12 suggests:
Shitari will return with a revived Dokoku.
The Shiba clan in this show is the same one in Bleach
The Jidai Geki illusion in the beginning Samurai Sentai Shinkenger Returns reflects how each of the families started out before becoming the Shinkengers
The sci-fi illusion in Shinkenger Returns is based on the dreams of the Origami.While the first six illusions seem to all be connected to the Shinkengers, the sci-fi scenario doesn't really fit any of them in particular. Therefore it must belong to the Origami, which were with the Shinkengers when they were captured. The Origami view themselves as the spaceship, which is itself struggling to survive along with the team.
The dream illusions in Shinkenger Returns take place in the Delusion World.The Ayakashi has the same abilities as the Moe Moe Z-Cunes. And the different illusions are the result of each of the individual Shinkengers' delusions overpowering everyone else's for a certain duration.
Dokoku is a Deconstruction of the typical Sentai Big Bad.Dokoku's Orcus on His Throne status is not simply a device for keeping him out of action. He is constantly raging and drowning his sorrows because there is absolutely nothing he can do in the Sanzu River aside from throwing temper tantrums and occasionally binding his subordinates. Fighting is all he is capable of doing; he isn't very smart, which is why he keeps Shitari around, and his Bad Boss tendencies bite him in the arse when he banishes Dayuu. He also seems to show some amount of affection for Dayuu, though it's hard to say how much exactly. He probably cared about them as much as his nature enables him to, but, being a creature born of boundless rage and frustration, he is bound by his nature. This, I think, was intentional, and I feel Dokoku gets a bit of a bad rep in the Sentai fanbase due to him being perceived as a Flat Character, when I think there is surprising depth to him.
There was another Origami with similar size/function to Ebi that got destroyed in the past.Ushi Origami, despite being the first Origami made, meshes prefectly with its successors to form Samurai Ha-Oh. This seems especially suspicious in Ebi Origami's case, as the makers of Ushi had no way of knowing about Ebi, and vice versa. The only solution to this is if the Origami were designed as a set, with the Ha-Oh combination, from the very beginning. [Perhaps they weren't all made immediately, but the designs were there, and Ushi was made taking them into account.] At some point between then and now, the large Origami that forms Ha-Oh's upper body, head etc was lost or destroyed, or possibly just never made. By coincidence or by reading up on previous Origami, Genta wound up making Ebi's functions perfectly plug that gap in the formation.