Ail, who adopts the human alias Seijuurou Ginga, is a central antagonist from the Makai Tree arc. He is an alien who arrives on Earth alongside his companion, An, as one of the last surviving members of their race. Their home planet was destroyed when its inhabitants became greedy and fought over the energy of the Makai Tree, the source of their life. The tree transported itself and the two survivors to Earth in the hope of teaching them the value of love over greed. To blend in and gather energy, Ail transforms into a human teenager with fair skin, neck-length orange hair, and purplish-blue eyes, though he retains a single earring. In his true alien form, his skin becomes light green, his hair grows long and shifts to a light blue with pink streaks, and his ears become pointed.

Ail has a complex and often contradictory personality. He is initially presented as prickly, sarcastic, and prone to jealousy, particularly when things do not go his way. He can also be charming and flirtatious, displaying a womanizing tendency that often creates tension with An. He is more outwardly friendly and inquisitive about human culture than his partner, though he frequently struggles to understand concepts like gift-giving. Ail possesses a fiercely competitive streak, especially towards Mamoru Chiba. He has a distorted, forceful view of love at the beginning, believing it should be taken rather than given freely. This flawed understanding drives much of his early behavior, leading him to target Mamoru out of jealousy and pursue his own romantic interest in Usagi Tsukino.

The primary motivation for Ail and An is survival. They require human life energy to feed the Makai Tree, which in turn sustains them. They pose as siblings and transfer students at Usagi's school, with Ail using his flute to summon Cardian monsters to drain energy from the populace. Despite their mission, Ail finds himself genuinely attracted to Usagi, developing a crush he tries to keep secret from An. This sets up a rivalry where An is drawn to Mamoru, creating a web of unrequited affections that complicates their energy-harvesting operations. Ail's jealousy manifests strongly during a school play when he is not cast as Prince Charming opposite Usagi, leading him to sabotage the event.

Throughout the story, Ail's key relationships define his arc. His bond with An is the most significant; they are partners, implied to be more than friends, yet their relationship is strained by jealousy and a lack of true understanding. His competitive dynamic with Mamoru forces him to confront his own shortcomings, while his growing affection for Usagi exposes him to genuine, selfless emotion. His role in the story shifts from a straightforward antagonist to a tragic figure who learns the error of his ways. In the climax, when the Makai Tree goes out of control, Ail protects Usagi, realizing that what he and An have been doing is wrong. He witnesses the power of true love through Sailor Moon and Mamoru. When the tree attempts to kill him, An sacrifices herself to save him. The tree then reveals it does not need any energy, but specifically the energy created by love. After Sailor Moon heals the tree, it revives An. Having learned the true meaning of love, Ail and An leave Earth with the rejuvenated Makai Tree to start a new, peaceful life.

In terms of abilities, Ail is skilled in combat and energy manipulation. His most distinctive tool is a flute, the music of which can summon Cardians from special cards. The melody from his flute also has an enchanting effect on humans, unconsciously attracting women to him. He can drain life energy directly from individuals and demonstrates considerable agility and strength in his alien form. His development is marked by moving from using these powers selfishly for survival to understanding the need for mutual care and love, a lesson that ultimately redeems him.