Sen

Sen is a mysterious monk who instructed Janis to follow Inuyasha and Kagome in feudal era. His true identity was Tsugumi, a human girl who gained Kamuitama from his husband, Datara. Under the influence of Gorai's Demon Blood Biding Spell, he was forced to listen his instruction and lured Janis to unseal Datara's seal.

History
Sen's first appearance was at the moment Janis was attacked by a yōkai near Higurashi Wellhouse, as she intended to visit Kagome due to several days of absence in school. After Sen eliminated the yōkai and cured Janis' wound, he gave an advise for her to find Kagome by going through the Bone-Eater's Well and returned to Sengoku jidai. Before Janis left modern era, Sen gave her two shikigami to help her reached to the save destination.

After Janis met Inuyasha and his friends at feudal era, once again Sen appeared himself below the Goshinboku and met Janis. Sen mentioned that Janis' Kamuitama was revived after the Shikon shard fused into her body. At the exact moment, Inuyasha and Miroku showed themselves at there and cut off the conversation between them, caused Sen had to left the place.

One day, Inuyasha with Janis and Kagome backed to modern era and heard Umao and Shikako escaped themselves, claimed that yōkai exist in Benten forest. When they entered Sen Shrine that situated in Benten forest, Sen mentioned once before that forest was covered with evil yōkai and he sealed it for preventing people got harmed. By following Sen's order, Janis took of five seals from five small shrines that placed everywhere in forest and defeated yōkai. When they returned to Sen Shrine and informed Sen, they saw a red glowing ball was located at Sen's behind.

As Inuyasha and the others successfully arrived at Datara Shrine, Sen showed himself in front of them and gave another instruction to open the door that lead to Datara's place. Datara's servants Mitsurugi and Sugagaki opened the door to let them entered, later Janis tried to pull out the Arrow of Sealing from Datara's chest. At sudden the white light glowed in front of their sight. When Inuyasha and the others woke up from unconscious, they realised they been used by Sen and Gorai.

In order to defeat Gorai, who was now forced to follow Naraku's words, they tried to visit the Tempest Tower. Unfortunately, the Demon Blood Biding Spell within Sen's body obeyed Gorai's instruction and also gained immortality, which was impossible to defeat Sen by using their powers. Unexpectedly, Kikyō appeared herself and gave a clue to let them find Sen's blood (that placed at Sen Shrine at modern era). Janis, Kagome and Inuyasha returned to modern era again to obtain Sen's blood, later they backed to feudal era to defeat Sen once again. Janis used her Kamuitama to bind his blood and his body together, and Sen turned into Tsugumi, slowly awoke from the spell. Inuyasha and the others felt extremely surprised that Sen's real identity is Tsugumi, and Tsugumi started to explain the whole events.

500 years ago after Tsugumi sealed Datara and killed her daughter during the wedding ceremony, Gorai put the Demon Blood Biding Spell onto her, made her Kamuitama tainted with evil demon blood and started to obey his words. She had waited this day that somebody like Janis would able to broke the spell and regained conscious.

Sine Inuyasha success to defeat Tsugumi, she knew that her life-span was limited. At the same moment Tsugumi felt happy she could see her daughter (Janis) at her last breath.

Quotes

 * "I am Sen. People call me, Monk Sen."
 * "I'm glad it was nothing serious, Daughter of Kamui. Then again...you're just an ordinary human now. Even a demon as weak as that one is deadly to you."
 * "Well, why did you come to this shrine, anyway? Kagome Higurashi is not here. She has not taken ill, either. If you wish to see Kagome, you must enter the well. Kagome is waiting for youon the other side of the well. As is your fate..."
 * "You have such a fine mother..."