Originally, Filo had the appearance of a small pink Filolial chick (much like an actual chick) and would sit on top of Naofumi's head when they were on the road. However Filo grew very rapidly and within a few days was the size of a normal Filolial making such actions impossible but allowing her to grow to a size so that she could be used to pull their cart, this was thanks to Naofumi's monster tamer shield, which he unlocked from some egg shell's his shield had absorbed.
Filo also has exceptionally fast legs, so much so in fact that she was able to beat a dragon in a foot race, despite many unfair attempts to make her lose. Filo's growth, however, was not finished at that point as a day later she had grown to exceed the size of a normal Filolial and upon interrogating Beloukas, he found that she was or maybe a "Filolial Queen." Naofumi, wanting to know more about what a Filolial Queen was, offered to have the slave trader take care of Filo for a few days, but, shortly after leaving her, he was called back due to a ruckus she had caused after being separated from her master. After Naofumi and Beloukas got into an argument, a strange voice was heard from the cage Filo was in, and much to everyone's surprise, Filo transformed herself into a small human girl with blonde hair and reached out for Naofumi.
Due to her constant transformation between her filolial queen and angel form, Naofumi tries to find magical clothes for her. After going on a quest with the magic shop owner to get materials, they are able to go to the tailor who then crafts her signature white and blue dress. Naofumi, Raphtalia and Filo then continue their peddling operations, saving Lerno Village in the process. When they arrive at Mirso Village and find the Zombie Dragon, Filo goes into a frenzy and is eaten by the undead dragon. Believing Filo is dead, Naofumi uses the curse series for the first time however, Filo is revealed to still be alive.
On the way back to Melromarc to treat Raphtalia's cursed burns they come across Melty. She and Filo become quick friends as Naofumi agrees to escort her to Melromarc. However, when Naofumi finds out that Melty is royalty, he forbids Filo from playing with her new best friend. Before the third wave he buys Filo her first weapon - metal claws for her talons and crafts her a hairpin. They eventually defeat the third wave and afterwards Erhard gives Filo gloves which magnifies her strength when in angel form.
Filo and Melty are reunited when Naofumi protects the princess from an ambush by Melromarc soldiers. This action labels the entire group as criminals as they are forced on the run from Melromarc soldiers and the other heroes. Motoyasu nearly captures Filo during an encounter but she uses the gloves Erhard got her to break free.
When the group is about to be caught at a friendly noble's house, Melty tells Filo to hide and sacrifices herself to save Filo and the rest of Naofumi's party. The group then save her from the malevolent noble who was about to torture her. In response, the noble unseals the Tyrant Dragon Rex and Naofumi's party baits it out of the town to confront it. As they are about to be overwhelmed, the Filolial Queen Fitoria shows up and defeats the dragon. She then takes the group to her territory.
While Naofumi's party is in Fitoria's territory, Fitoria suddenly holds Melty hostage and orders Filo to fight her in order to gauge her "worthiness". During this intense battle, Fitoria trained Filo how to fight properly and Filo eventually proved her worth. As a reward, Filo is crowned as a true Filolial Queen and is designated as Fitoria's successor.
After Fitoria has further discussion with Naofumi, she drops the party off near Motoyasu. They have a quick fight before they are attacked by the pope. They eventually win and Naofumi's party is released from all false charges by Queen Mirellia.
With the group no longer being considered fugitives, they are able to conduct their class-up ceremony which breaks the level 40 limit. However, before they are able to choose which kind of class-up they want to pursue, the cowlick Fitoria gave Filo interferes with the process and chooses a special class-up path for both Raphtalia and Filo. After attending a conference of the Legendary Heroes, Naofumi's party including Filo head to Cal Mira Archipelago to level-up. After doubling their levels, Filo discovers an underwater temple and dragon hourglass. Thanks to this, Melromarc and the Heroes were able to prepare and defeat the wave which was about to occur.
After the Spirit Tortoise was unsealed, Filo was essential in helping defend Lerno Village from the Spirit Tortoise's familiars. Later on, she and Raphtalia were able to cut off the Spirit Tortoise's head.
As the Spirit Tortoise started making its way towards Melromarc, Naofumi's party (including Filo) were responsible for stopping it or delaying as much as possible. Talking through Filo, Fitoria was able to warn the heroes and arrive just in time to face off against the Guardian Beast by herself. Naofumi's party and some of Melromarc's forces journeyed within the Spirit Tortoise to defeat it. Filo and her innate use of Hengen Muso became invaluable in keeping the forces alive. When they confronted the enemy behind the Spirit Tortoise's unsealing, Naofumi's party including Filo chased after him to Glass' World. However, the group became separated since the dimensional portal was trapped.
After being transported to Glass' World, Filo found herself reset to level 1. In addition, she had transformed into a humming falcon instead of a filolial. Being a unique monster to Glass' World, she was captured by a rich noble and put on display in some type of circus. Thanks to Raph-chan, Naofumi, Rishia, and Kizuna were able to find and rescue her. This traumatic experience stayed with Filo for some time until Naofumi was able to comfort her. Over time, Filo started to level-up and gain more abilities in her humming fairy form. She also learned how to use music magic.
During the final confrontation with Kyo, Naofumi used All Sacrifice Aura on Raphtalia and Filo. While this gave them great power to defeat the enemy, this also placed a strong curse on both of them. In the end, they were able to defeat Kyo and return to their own world, however their stats were reduced to 1/3 of what they should be which would last 2-3 months.
In order to obtain money to buy villagers who were originally from Lurolona Village, Naofumi decides to enter himself, Raphtalia and Filo for group fights within a Zeltoble coliseum. Thanks to Hickwaal and Beloukas' Uncle's influence, most of their fights are easy wins. However, their last battle in the tournament ended up being against Sadeena as "Nadia". After a difficult battle, Raphtalia convinced Sadeena to throw the fight but then all four are immediately pitted against S'yne as "Murder Pierrot". Partially thanks to Filo's music magic which was immune to magic suppression, they were able to defeat S'yne in battle.
In the aftermath of the Spirit Tortoise Catastrophe and Malty's betrayal to Motoyasu, Motoyasu fell into a deep depression. Eventually, Filo attempts to cheer up the broken hero. However, as a result of Motoyasu's broken state, he became obsessed with Filo and started considering all other women as "pigs". At this point, Naofumi runs away from Motoyasu with Filo and Raphtalia to protect themselves. Later on, after defeating the Otherworld Invaders and capturing Ren with Motoyasu, Motoyasu steals Filo's beloved carriage.
As the village was setting up, they were gifted a dragon egg which Naofumi hatched as Gaelion. With filolials and dragons being natural enemies, Filo and Gaelion started fighting aggressively for Naofumi's affection. However, at one point, Gaelion consumed the Demon Dragon Emperor's dragon core which resulted in the baby dragon being possessed by the Demon Dragon Emperor. The Demon Dragon Emperor then used the zombie dragon core Filo had swallowed as a medium to siphon her levels into himself. Eventually, they were able to stop the siphon and defeat the Demon Dragon, however Filo's lost levels were permanent.
Using Filo as her spokesperson, Fitoria asked Naofumi to take care of a filolial threat and gives Filo a powerful blessing which slightly offset her lost levels.
With the Q'ten Lo quest over, Naofumi finally starts looking at the quest Fitoria had assigned him. It turns out that the threat was Motoyasu who was training an army of filolials thanks to his obsession with Filo. Motoyasu forces Naofumi in a race with Filo on the line as the reward. Naofumi wins thanks to learning how to cast Liberation-class magic. However, the jealousy-fuelled Motoyasu rampages and uses his curse series weapons disrupt Naofumi's party. Using Motoyasu's obsession with Filo, Naofumi convinces Filo to talk down the Spear Hero and convinces him to join the other heroes at Naofumi's Village.
Later on, the Heroes' forces (including Filo) fight against the Guardian Beast called the Phoenix.
Around this time Filo has become an idol - singing throughout the lands and gaining a massive following.
Thanks to her previous experience travelling to other worlds, Filo is included in the party that will travel to Glass' World to save the heroes there. They end up recovering several of the stolen Vassal Weapons and freeing Kizuna.
After travelling to the newly-revived Demon Dragon Emperor's territory, the Demon Dragon finds that one of her commanders is disobeying her orders. The Demon Dragon then strips the disobeying commander of the power bestowed to her and then forces it on Filo. This changes Filo's race in Glass' World from Humming Fairy to Heavenly King and gives a massive power-up. However, since Filo despises the Demon Dragon, she also hates using the Demon Dragon's power. The only ability she regularly uses is her new power of flight.