- 3days' slogan.(src)
3days ~Till Death Do Us Part~ (3days ~満ちてゆく刻の彼方で~ 3days ~Michiteyuku Toki no Kanata de~) is the second product of Lass and the spiritual prequel of 11eyes. The story revolves around an endless cycle of three days in which the third day ends with the deaths of the protagonists.
In Ayashino city, women are easy targets at night by the hand of a serial killer, who kills his victims in the most brutal way possible; Miyu Hiiragi, a student of Ayashino Academy was the most recent target. Ryo Takanashi, the protagonist of the story was enjoying his normal daily life until he and the killer crossed path. While spending time with his childhood friend Tamaki, the killer infiltrated Ryo's house and mercilessly gouged Tamaki's heart out and killed Ryo for getting in his way. The next morning, Ryo woke up normally, thinking all that happened was only a bad dream. However, this was the start of the endless time loop. Ryo has three days to live before being killed, then all is rewound again and again. After a few loops, Ryo came to understand that there was a connection between him and the killer, as well as the girl Miyu...
- Ryo Takanashi (高梨 亮 Takanashi Ryo). The protagonist of 3days. He lives with his paternal female cousin, Narumi. He is later revealed to be the reincarnation of an Onmyoji named Ryouichi Kusakabe, who died in battle 15 years ago and was resurrected by the Clock of Kairos. The item is also responsible for rewinding time back to the morning of October 16 after Ryo is killed by Walter Dietrich on the night of October 18. This thus started the endless 3 days cycle and hence the title.
- Tamaki Fujimi (藤見 たまき Fujimi Tamaki). A childhood friend and also love interest of Ryo. She usually make early calls to wake Ryo up in the morning. Later in the story, she is revealed to contain the Fragment of the Emerald Tablet in her body, which explained why she was targeted by Walter Dietrich. The reason for the presence of the Fragment inside her body was explained as Ryo regained his past life memories. After the first battle with Walter, the fatally injured Ryouichi asked Miyu to dispose of the Fragment and the Necronomicron. Miyu then used the Clock of Kairos to open a time rift where she dumped the artifacts. The Fragment, while trapped inside the time rift, cannot manifest itself physically so it took form inside the womb of Tamaki's ancestor, who gained the power to heal sickness and injuries and known as the Green Priestess. This power was passed down from mother to daughter and the mother loses her power as the result.
- Miyu Hiiragi (柊 美柚 Hiiragi Miyu). A senior at Ryo's school and was apparently killed at the very beginning of the story. She was, in fact, a homunculus created by Simon Faustus 1000 years before the events of 3days to replace his wife, Helena. She stayed inside Simon's castle for about 500 years before being discovered by Walter. While staying inside the castle, she simply cannot be killed as she will regenerate immediately any damaged done to her body. She told Ryouichi that being away from the castle slowly reduces her invincibility. Ryouichi, while looking at her with his spiritual eyes, amazed that the spells that Simon weaved to create her is as powerful as a dragon. Simon was intending to give her the name Helena, but he failed to do so. She told Ryouichi the reason was because only the one that truly need her as she is could name her. Since Simon intention was for her to replace his death wife, he thus do not truly need her for who she is. Walter called her Namenlos (ナームルス Namurusu, lit. "Nameless" in German) due to Simon failing to name her. Due to be in possession of the Clock of Kairos, she was later captured by Walter Dietrich and brought to Germany for research. As Walter heard of the presence of the Fragment of the Emerald Tablet inside Ryouichi's research facility in Japan during World War II, he decided to traveled there taking her along with the Clock of Kairos to trade for the Fragment. Ryouichi Kusakabe, who sympathized and fell in love with her, set her free by giving her a name and attempted to take her far away from Walter's clutches. However, they engaged Walter on the run and, although victorious, Ryouichi was killed after the battle. Miyu patiently waited for Ryouichi's resurrection and finally met him thirty five years later. Unfortunately, Walter was also resurrected at the time and they battled once more. The result of the battle was the same as the previous one, but this time, Miyu use the Clock of Kairos to resurrect Ryouichi.
- Nanako Chikami (千神 奈々子 Chikami Nanako). A close friend of Miyu. Among the main heroines, her role in the story was the most minor. However, in the finale, she became Ryo's love interest. She has been presented in all of Lass' works except for 11eyes. Her reason for not being presented in 11eyes could be that in Festa!! she was finally made into a plot involvement heroine whereas in other games, she only cameo as minor role. In one scene, she mentioned to Ryo about her past, about the town in Lass first work, Ao to Ao no Shizuku and about her confession to and subsequent rejection from the protagonist of Ao to Ao no Shizuku. She is mentioned in 11eyes Resona Forma as Takahiro's wife.
- Tsukiko Hirohara (広原 月子 Hirohara Tsukiko). A cheerful and knowledgeable girl at Ryo's school and a good friend with Tamaki. She is regarded as the "Number One Troublemaker" and the "Humanoid Hurricane" at the institution. Her most noticeable traits involving her twin tails, the goth-loli dress in addition to the an attitude of ignoring everyone around her while she talks nonstop. She is the only club member of the school occult club, which she created. Due to her vast knowledge about the occult, Ryo consulted her in a few scene about the black coat man and the meaning of Kairos. In addition, she is the older cousin of Yukiko Hirohara who is admired and mentioned in 11eyes.
- Rika Azuma (吾妻 梨花 Azuma Rika). A strange and quiet girl at Ryo's school. She appear to be unstable, self-isolating, and self-wounding. Her most noticeable trait is the eyepatch. She later told Ryo that when she was younger, she appeared to have developed another split personality, which she referred to as "the demon", and acted crazy when it took over. Because of this, she was shunned by her parents and was forced to live in a downgraded apartment alone. Although unwillingly, she also accepted living in isolation so as not to involuntarily hurt her sister Ruka. In actuality, Rika is the new host body for Walter Dietrich, who attempted to use her body to regain power until he was strong enough to find another host. However, her family's magical bloodline suppressed him for ten years.
- Ruka Azuma (吾妻 瑠花 Azuma Ruka). Ruka is a cheerful girl whom Ryo often meets in the park or at the train station and was also the younger sister of Rika. Due to Rika's expulsion from the family, Ruka often plays with little animals. In one time loop, Ruka was easily taken over by alter, implying that her magic potential is very low or that she is too young to control a psychotic Walter.
- Ryouichi Kusakabe (草壁 遼一 Kusakabe Ryouichi). The past self of Ryo. He was a magic researcher inside a facility masqueraded as an Asylum in World War II Japan. The reason for the job was because he was expelled from his clan as a heretic by trying to incorporate Western sorcery into Onmyodou. He later fell in love with Miyu and decided to start a new life with her. When he attempted to run away with Miyu, he encountered Walter and engaged him in battle. Although Ryouichi succeeded in destroying Walter's body, he was gravely injured and died afterwards. Thirty five years later, he reincarnated as a young boy and found Miyu in Ayashino City. Unfortunately, Walter also revived, inside the body of a young Ryo, and he was forced to battle Walter again. The result of the battle was the same as the previous one. However, before Ryouichi died, Miyu transferred his soul into Ryo's body and use the Clock of Kairos to resurrect him. Unfortunately, the present Ryo lost all his memories as a result. He is mentioned a coupled of time in 11eyes by Misao and Misuzu as the creator of most of the forbidden techniques they used and is also an acquaintance of Kanji Amami, Shuu Amami's grandfather.
- Narumi Takanashi (高梨 成美 Takanashi Narumi). Ryo's older cousin. She enjoys teasing Ryo, but always care for him. She is a journalist. In the infinite 3 days arc, she is always going out of town for her assignment on the third day morning, which spare her from being killed by the masked person. Her family, which consisted of her and her father, adopted Ryo after his parents was killed by Walter while he was mental parasiting on Ryo. Her mother passed away when she was young, and her father just died the year before the story took place due to cancer. After adopting Ryo, she and her family told Ryo that his parents was killed in a car accident instead of being cold blooded murdered.
- Kenji Tomioka (富岡 健二 Tomioka Kenji). A large man, who is the student adviser at Ryo's school. He usually carry a bamboo sword around to threaten the students and always tell them to join sports clubs to gain body builds like him, frightening most of the student at the academy. He was killed by Miyu, mistaking him for a host of Walter.
- Yuuza Azuma (吾妻 友哉 Azuma Yuuza). The missing brother of Rika and Ruka. He was the first reincarnation of Ryouichi Kusakabe by his reincarnation technique. As a elementary school student, he recovered his past life memories and seek out Miyu during the first rise of Walter when Walter was taking control of Ryo Takanashi's body. In a battle that was ensure later at the local park inside Walter's Marble Reality, he defeated Walter despite the disadvantages as not being as an adult and not having as much power as his past body. Unfortunately, due to such lacks of power, he was fatally injured while Walter got away. Miyu revive him by using the Clock of Kairos into Ryo Takanashi's body, whose soul was eaten by Walter as he was parasiting on the child's mind.
- Walter Dietrich (ヴァルター・ディートリヒ Varuta Deitorihi). Also known as Hochfart, a member of the Magic Association of Thule. He was promoted to Thule from the S.S. He wanted to combine the power of the Emerald Fragment, the Key of Hades and the Clock of Kairos to attain immortality, and then proceed with conquering the world. However, at the end of World War II, his body was destroyed by Ryouichi Kusakabe and was forced to live parasitically inside animals. Thirty years later, he managed to mentally parasitize a young Ryo Tanakanashi and attempted to resume his plan. However, Ryouichi managed to expel his soul from Ryo's body and Walter was forced to wait until his power regained to use Mental Parasitism again. Five years later, he succeeded in parasitizing Rika Azuma, but due to her magic bloodline, he was suppressed for ten years and could only take over Rika when she was at her weakest. During his short periods of taking over, he roamed around Ayashino City at night and killed residents to gain more power. His personality depicts a sadist and a Nazi at his worst. He would gruesomely kill anyone who got in his way or people who he thought would be necessary for him to gain more power. In fact, the reason that he made it into Thule was because of his genius and ambition for power. He claimed that one of his ancestor was an inquisitor during the Witch Hunt. His cruelty is demonstrated by the bloody way he killed Ryo and Tamaki every time in the infinite three days arc. As he was parasiting on the young Ryo Takanashi's mind, he ripped out the hearts of Ryo's parents to sacrifice them to the Necronomicron for power as he no longer had the Fragment of the Emerald Tablet. He also ripped out the womb of many female victims who has magical potential to sacrifice to the Necronomicron right before the story begins.
- Clock of Kairos (カイロスの時計 Kairosu no Tokei). A clock that can manipulate time. According to Miyu Hiiragi, the clock is also a homunculus created by Simon that has the ability to calculate outcome and consequence of events but lack soul and mind. Due to its unique origin, this clock is almost indestructible. The clock was created so that only Miyu can utilize its power.
- Nail of Helena (ヘレナの聖釘 Herena no Seitei). Walter forged the nail into bullets which he shot at Ryouichi during their first battle after Ryouichi transformed into an oni. The bullets' holy property caused great damages to Ryouichi's demonic body.
- Key of Hades (冥王の鍵 Meiou no Kagi). Also known as the Necronomicron. A grimoire that is described as having a malevolent aura with a cover made of human skin with a eerie looking face on it. Powerful Larvaes based spells are written on this grimoire which Walter used to control and manipulate Larvaes inside his Specialized Bounded Field and to create undead creatures from the bodies of his victims. Due to the grimoire contain spells that require high magical input, Walter either needs the Fragment of the Emerald Tablet or a sacrifice to power the spells.
- Emerald Fragment (翠玉碑の欠片 Suigyokuhi no Kakera). The one and, possibly, only fragment of the Emerald Tablet that still retains the power of the original object.