It almost seems like the relationship between Mana and Makoto when they first meet is similar to that of Hibiki and Tsubasa from Symphogear. It doesn't help Makoto had a somewhat similar back story to Tsubasa.
Episode 1: When told by Charle to transform, the first thing Mana does is yell "Henshin!" and pose like Kamen Rider #1.
Speaking of Kamen Rider, Doki Doki!'s motif of four heroes named after the suits of cards is exactly the same as Kamen Rider Blade . Cure Sword even shares the same last name (Makoto Kenzaki) and card suit as Blade's main character (Kazuma Kenzaki) to the point of being written with the same kanji!
The series has a bit more in common with J.A.K.Q. Dengekitai, especially with the fact that Cure Ace shows up and shows everyone up, just like Big One.
And to top it all, the fanartists are having alot ot fun comparing Cure Heart's transformation with that of Kamen Rider Beast with both having the four letter spell out (L-O-V-E vs. L-I-O-N)
Not only that, Cure Heart new finisher move that involve using a bow is the same as how Kamen Rider Chalice using his bow as his finisher.
Episode 21: When the Precures and Jonathan arrive at the Trump Kingdom, the Selfish Trio delivers a familiar comment:
Ira: "What's that? A bird?"
Mamo: "A meteor?"
Bel: "No. It's Precure."
Episode 23 includes Ai wo Torimodosenote "Take back the love" word for word as a part of the title.
A new team member taking away the leader's transformation item and forcing them to fight as a normal human has already happened before.
Cure Ace's transformation sequence has a lot of similar body shots to the ones used in Sailor Moon, another product of Toei. The fire based theme of the transformation may be one to Shana, who is also voiced by Rie Kugimiya and has fire erupt around her when she gets into battle mode.
Episode 25: Mamo as Cutie Madame pretends to be a hero and causes a civilian to fall from a building, so she can rescue him. Zoisite, disguised as Sailor Moon, did the same thing. Her transformation pose even loos like a mirrored version of Sailor Moon's.
Now all the three regalia are revealed, they share a great deal of similarities with the pure heart talismans of Sailor Moon fame. The Miracle Dragons Glaive equates to Uranus' Space Sword, representing strength. The Magical Lovely Pad ties to Pluto's Garnet Orb, surprisingly, rather than Neptune's mirror, representing benevolence. The Eternal Golden Crown is equivalent to Neptune's Deep Aqua Mirror, representing wisdom. These talismans were in turn based on the three imperial treasures of Japan, so the resemblance could be accidental.