Luna's deck sucks, here's how to fix it
So I've got a lot to say about Ruka/Luna and her role in the story, mostly how I think it could have been better. But I'll start with the first way that the writers fail Luna: her deck.
If you play the TCG, you may already know that Luna is one of the few main cast duelists that never got an archetype associated with her. By this point in the franchise, every character has their own archetype or two associated with them, yet Luna doesn't use any archetype specific cards (unless you count Kuribon). She has a loose fairy forest type theme that is a mix of plants, fairies, and beasts. This isn't too out of the ordinary for characters, Akiza also had no real archetype during the series (just a lot of plant/rose themed cards), but she and most others in that state got some sort of archetype retroactively made around their deck (in Akiza's case, the Rose Dragons). Luna has not received any support.
Luna's ace monster is Ancient Fairy Dragon, who in the series, she had a strong connection to. And despite being the weakest attack wise of the Signer dragons, AFD's effect gave her the strongest counter against the Earthbound Gods in the first arc (which is why she had to get written out for most of it). In fact, this effect would be so strong that AFD would get banned irl for several years until the card got an errata. And possibly because of this, AFD is still the ONLY Signer dragon to never get an upgraded form.
Now let's talk about Luna's duel against Professor Frank. This is Luna's first showing as a duelist especially after being hyped up as a former dueling prodigy. Even with the very loose deck, there is a bit of a strategy there. Luna use Ancient Forest to attempt to lock her opponent out of attacking, then uses life point gain and loss effects to slowly burn her opponent. Eventually the duel ends in a draw with Luna using Oberon's Prank in combo with Kuribon's LP gain effect. And that is the end of the ONLY solo duel Luna gets in the series.
Looking back on this duel after having finally played Yugioh, I had the sudden realization that Oberon's Prank was an anime only card with an awful effect made just so Luna could force a draw. Oberon's Prank is a trap card that makes it so that any LP gain effects used on your opponent are negated, and both players take damage equal to the LP that would have been gained. The closest equivalent to Oberon's Prank irl is Bad Reaction to Simochi, which only inflicts damage to the opponent. Simochi was also used by Luna in the World Championship games and is probably the intended way to use Kuribon's LP gain effect. So the only reason I can think for why they would write the duel in this way would be because they really wanted Luna to tie/lose. In a narrative sense, I get wanting to show that Luna is kind and would rather force a draw than let her opponent get eaten by a dragon. But also, she wasn't going to win the duel at that point, let her run Simochi and get a win. Or make it look like there was a choice in the matter.
(IMO, if the dragon wants to eat the creepy psychologist, soup's on.)
So if I were to fix Luna's deck, the first thing is giving her a Naturia/Vernusylph deck.
Naturia is a Synchro and Fusion focused deck that is composed of Earth attribute monsters with the goal of controlling the opponent's movements. A couple of the Naturia cards would have already been made by the time of 5Ds. Naturia works for Luna for a couple reasons; the control style is a good contrast to Leo's combo focused deck, they're a bunch of cute critters that fit the fairy forest theme Luna was going for, and the archetype's story itself is also related to the Naturia protecting their home forest (as Luna does for the card spirit world).
Their boss monster is also named Leo and I just think that's funny.
Maybe the writers did consider Naturia and decided against it for whatever reasons (didn't want another majority plant player after Akiza, knew Luna would be too much of a menace with Naturia Beast, wanted to save the cards for the Duel Terminal arcade game, etc.).
Supporting the deck further would be the Vernusylph archetype, which are a small archetype of Earth fairy monsters that offer support to other Earth monsters. They're a relatively new archetype so some effects may be a little strong for 5Ds era (especially Vera). But they fit into Naturia well and would have really solidified the fairy forest theme. Also them being Earth support in general means that they can support Powertool Dragon and many of Leo's Morphtronics in tag duels (also a couple of Team 5Ds use Earth monsters so it would make Luna fit well into a lot of tag duels). And despite being a Light attribute, AFD fits into the deck.
And another monster I think would fit would be Circle of the Fairies (also a relatively new card). This one throws off the Earth attribute focus a bit, but offers support for plants and insect types. Also more burn and LP gain effects for Luna. And it and the other Circular monsters keep up the fae theme being based around fairy circles.
That's my opinion on what Luna should play. It's not too late for Luna to get an associated archetype, there's a couple of characters who get different archetypes in later games, like Tea playing Witchcrafter in Duel Links and Blair getting Lightsworn in Tag Force. Or Ishizu who's deck retrains created one of the most powerful decks in history. AFD is also long overdue for an upgrade/support after being off the banlist for a couple years now. And so Konami should make Luna's deck absolutely broken as an apology.
