Her tattoo is of a card drawn with a nugget on it.
Tou-chan says it was his inspiration for making Monstermon in the first place. With her twin also having a card theme for his tattoo -though instead of a nugget, it was an apple*, of all things- he began making and designing the battle cards for them. At first, the cards had merely been a little something of a family game for them but eventually, it caught on. Family members and friend's children would see the cards they'd play with and be engrossed and ask. The ruder ones would swipe it from their hand with no care at all.
Though, that stopped fairly quickly. Just...not for the reason you may think.
(She remembers her father laughing at the time. Picture her, a little toddler with a kaeru plushie, just shy from being three years old, punching a ten-year-old's nose and subsequently throwing the rubix cube her brother had been holding in the exact same location.
Her brother sniffled at first but saw the wailing pre-teen clutching his nose, and laughed.)
It's a funny thing, to have made a card game out of their soul tattoos, but Lily figures it was fine all the same.
Shame she couldn't use her 'The Nugget' card in public, it was one of the first ever Monstermon cards her dad had made, therefore making it an unofficial card.
(Well, that and how OP she'd made the card's abilities to be. Really, placing it down would be an instant win. Taking half of the opponent's life once placed down and if not destroyed by the end of the turn, take the remaining half of the opponent's life.)
The rules had changed since then as well, so her first ever Monstermon card was kept safely behind the glass of a picture frame on her shelf.
Lily wondered if her soulmate knew they were partially the reason the top-hit card game of all time came into existence.
His tattoo was of a frog in a detective's uniform.
He asked what it was, and where he could find it. Gramma had told him one time that frogs would typically be found under the ground, as he clumsily shoved the slop they had for dinner in his mouth.
He was grown-up now, he could handle feeding himself.
That's what he told his Gramma, at three years old.
Subsequently, at that age, he begged for many beach toys from his Gramma. Especially the ones that looked like a spoon! He wanted to find these frogs and see what made them so special to his soulmate!
Around his many excavations, he would see fellow children sitting on benches and tables faced against each other.
They were playing a game. A card game. And Nugget couldn't help but feel a connection. He wanted those cards, as well.
No, he needed them.
But he never stopped digging.
(He totally forgot about the other hint of his soulmate's interests. The detective outfit the frog wore meant that his soulmate was interested in detective work, missing cases and murder cases and the like.
He did eventually wonder if he was supposed to be worried about that specific interest. Would his soulmate be in danger for their hunger for the truth?)
Nugget wondered if his soulmate knew they were the reason for all the many potholes and Nugget Caves all around town.