Myōga

is a flea yōkai who was a servant of the Inu no Taishō until his death, and then acted as a servant for Inuyasha, providing him with information on current events, foes, and the shards of the Shikon no Tama.

History
Assigned to protect Tessaiga's hiding place in the grave of Inuyasha's father, he runs away when Sesshōmaru comes there in search of the sword. Myōga usually leaves the group regularly to search the land for useful information, and often shows up again at unexpected moments. He also runs away if there is any danger and is always found somewhere where it is safest.

Naraku's Barrier
Inuyasha and his crew desperately sought ways to pass Naraku's barrier. When Inuyasha traveled to meet Tōtōsai for advice, Myōga learned how to strengthen Tessaiga and achieve the feat.

Myōga informed Inuyasha he needed to travel to a specific island with bat Daiyōkai. There, they used Hanyō to power their own protection barrier similar to Naraku's. Myōga informed Inuyasha he would find Taigokumaru there, and upon having Tessaiga drink his blood, it would be strong enough to break Naraku's barrier.

Finale
In the series finale, Myōga chooses to remain living with Tōtōsai.

Personality
Myōga often flees before or during a battle, which the others recognize as a sign of pending danger; his mere presence in any area is enough to determine its safety. Myōga particularly enjoys drinking yōkai blood, and actually saves Inuyasha's life at one point by drinking a spider yōkai's venom out of his blood. He can save the others in a similar manner, but often gets squished for drinking their blood without permission. He is also good friends with Tōtōsai, and often spends time with him when he is not with Inuyasha's group.

Powers & Abilities

 * Blood Consumption: As a flea demon, Myōga drinks the blood of living creatures - human and yōkai; doing so greatly increases his size to the point he's the size of a human child.
 * Poison Digestion: Myōga has, when it is needed, sucked poison out of his allies, the poison he has drank appears to have no effect on him.
 * Enhanced Jumping: Myōga seems capable of jumping extremely high as shown when was able to he reached Miroku, who was high up in the air on Kirara.
 * Information Gathering: Due to his small size and connections, Myōga can get information on just about anything he want whether by eavesdropping on people or hearing it from a friend.

Relationships
Myōga faithfully served the Great Dog Demon for many years, serving as the voice of reason towards reckless actions. Myōga knows of almost all his secrets and the stories of the mighty battles he fought in. It appeared he had no problem with Myōga drinking his blood, which the flea demon said was delicious. Following his death, Myōga was brought to tears.
 * Inu no Taishō

Myōga has known Inuyasha since the half-demon's birth, always addressing him as "Lord Inuyasha" as a sign of respect. However, Myōga has the habit of trying to suck his blood when they meet, only to be squashed. Just like with the Great Dog Demon, Myōga will often try to reason with Inuyasha, to keep him from performing reckless actions. Inuyasha tolerates Myōga for the advice he can give, but is constantly annoyed by his habit of running away from danger. Myōga is sort of a counterpart to Inuyasha of what Jaken is to Sesshōmaru- a knowledgeable and diminutive (in Myōga's case microscopic) servant who is devoted to his master, but constantly ill-treated. However, in Myōga's case at least some of it is deserved because he is much less loyal than Jaken (as he is a complete coward), although he does not suffer Jaken's constant death-threats from Sesshōmaru.
 * Inuyasha

Myōga is an old acquaintance of the swordsmith, often being found hiding out from danger in the volcano the demon calls home. Tōtōsai often makes fun of Myōga for running away, but it seems both have a good bond of friendship between them. After the three year time skip at the end of the series, Tōtōsai continues to allow Myōga to live with him.
 * Tōtōsai

Anime vs. Manga
In the anime series, he is engaged to another flea yōkai named Shōga, but continually runs from her to avoid the marriage.

Trivia

 * Ironically, Myōga's name means divine protection, but as soon as he senses danger he flees (which has been witnessed throughout the series).
 * Myōga has.
 * Myōga used to be a companion of Inuyasha's father, the Inu no Taishō
 * Myōga is the only yōkai in the series so far to have regular human-shaped ears while other yōkais have pointy ones.
 * Myōga often gives vital information, but flees usually immediately afterwards most likely far away from the battle.
 * Having been a faithful companion of Inuyasha and Sesshōmaru's father for many years and already appearing to be rather aged at that time, Myōga is one of the oldest characters in the series.
 * According to Rumiko Takahashi, Myōga has the potential ability to increase his size to 2 meters long while sucking in blood.
 * Myōga is about 7 millimeters in height, slightly smaller than Inuyasha's Beads of Subjugation.
 * Despite his servitude, it seems as though Myōga was absent much in Inuyasha's early life; however it could be due to the latter's harsh life and the flea demon never felt safe around him. It is understandable that the two crossed paths before (seeing how Inuyasha recognizes Myōga).
 * Myōga is simular in appearance and personality to Happosai from Ranma ½. Both of whom are voiced by Paul Dobson.
 * Myōga is voiced by Kenichi Otaga, who also voiced Genma Saotome from Ranma ½ and Ataru's Father in Urusei Yatsura. Coincidentally, Kappei Yamaguchi (Inuyasha) voiced Genma's son, Ranma Saotome.