Yvonne's Grand Lorde Guignol outfit has her wear cross earrings and a silver cross over her neck. Due to her love of puppets, one can think that the crosses are symbolic of the crossbars used for marionettes, but the Theater of the Grand Guignol where she gets her namesake for was originally a church.
Also at a first glance, one would think Yvonne's use of Shaddolls is because of the whole puppetry gimmick...but when you look closer the original names of the Shaddolls comes from Jewish mythology/Judaism, with the name of El Shaddol being based on El-Shaddai or "God Almighty". Again tying in that the Grande Guignol is a church.
A third one, the theater of the Grand Guignol was repurposed from a church.
It seems odd for Yuto's sign and Serenity's Animal Motif to be a heron. But it actually makes lots of sense once one breaks it down:
Herons were said to be known as messengers in mythology. Yuto's appearance in the anime was what shifted the tone of the entire series. Plus, it is him who tells Yuya what is going on with the multiple dimensions and how Academia invaded Heartland. Likewise, Serenity is known as the one who spews out a lot of exposition.
They represent stillness and tranquility: both of them have calm attitudes compared to their brothers. It also represents waiting for the right time to strike; Yuto in comparison to Shun, does not needlessly pick fights with Academia and only duels when otherwise necessary.
A heron is known as a symbol of water. Yuto's affinity is of water and his 'mother' from the Sunken Realm is Llorona.
Herons are devoted to their families. Considering Yuto's situation at this time, this is all the more fitting.
They were symbolic of helping guide souls into the afterlife. Fitting since Yuto uses a deck consisted of fallen souls inhabiting armor and Serenity is part of a guild that repurposes people.
During their duel against Zarc and Yuya, both Yvonne and Yusho make a Non Sequitur, *Thud* by stating something from Ray Bradbury ("I Sing the Body Electric!" for Yusho and "Let's All Kill Constance" by Yvonne). While it looks like utter nonsense at first, the themes of the works connect to the person this is said to.
Yusho's reference is about a family who adopts a robotic caretaker as a replacement mother. The daughter of the family hates the robot due to her believing that the robot will just "abandon" (die) like her real mother did. The "replacement" comes from how Yvonne briefly sees her brother in Yusho and her snarky and cold attitude stems from knowing that she will have to kill him and she doesn't want to be "abandoned" by the closest thing she'll ever have to Xavier. Moreover, the daughter realizes the robot grandmother truly loves her after said grandmother shoves the daughter out of the way from a moving truck and reveals that she's right away. In a way, Yusho is revived and revealed to be right as rain even after Yvonne kills him.
Yvonne's reference is a murder-mystery about an aging Hollywood actress named Constance who is being targeted by a killer alongside many once-famous stars with many of the people listed alongside her also killed off. This one relates to how people close to Yusho (Yuya and Yuto) have been killed off (by Yuzu) but also because Zarc is also killing him in the future. And given the comments of many of the people watching the duel, they're all taking part in Yvonne's scheme to kill Yusho.
When you think about it, why drag out the tag team duel with the fight on the carousel? Then you consider Yvonne's thought process: She's going to kill Yusho sooner or later so she wants to drag out the duel so she doesn't have to think about it.
Yusho's reaction to learning that "a new purpose awaits him" is to laugh...but then remember that one piece of advice he gave to Yuya is "When you feel like crying, laugh". This adds another layer of how fucked up Yvonne killing him is; he's trying to hide his tears by laughing at what he's gotten himself into.
One of Yusho's favorite films is Ladyhawke, about a knight and a lady cursed into different forms — a knight is a human at day and wolf at night, his love a hawk by day and human by night — who still try to stay together even after they have been cursed for two years. Then you realize that this is a story of Yusho's life; he and Yoko are in two different worlds but his love for her is still everlasting despite the situation he put himself through.
Many of the songs that are sung or mentioned in the story actually have a lot of hints and meanings on who the song is for.
"You're Not Here": In the game, this is sung in Heather Mason's point of view, struggling on her own after dealing with the death of her father. In Mors Omnibus, this is sung two chapters after Yvonne killed Yusho, mirroring how much he idolized him and must struggle with him gone.
