In 1171 Yesugei takes Temujin to the tribe of Kuda — Ungirats. The official reason — the search for a bride for Temujin. In reality Yesugei had a purpose — to save his son-heir in case of war and search for allies.
This is indicated by the fact that Temujin was left for a whole year with relatives. Even according to steppe customs Temujin was too young to look for a bride. This was different. Perhaps, the Taijiuts strengthened and wanted to destroy Esugei’s family as a pretender to the Mongol throne.
Yesugei left his son with the leader of the Ungirats Day-Sechen, whose daughter 10-year-old Borte took a liking to Yesugei. It is unlikely that she was betrothed, as according to «Jami at-tawarikhu» by Rashid-ad-Din Day-Sechen did not want to be related to Yesugei. Day-Sechen did not bear his name in vain — the epithet «Sechen» (Mong. setsen) translates as «wise». He knew Zhurzhen and Chinese languages, corresponded with Jin officials, knew Chinese rites and traditions, had a library. Day-Sechen knew a lot about what was going on in the steppe. And about the intrigue that was going on around Yesugei.
Borte-fujin, Borte-uchjin (fujin in Chinese «Mistress» ; 1161 — 1230) — the senior wife of Temujin (Genghis Khan); daughter of Day-Sechen (Dai-noyon) from a sort of Ungirat and his wife Tsotan.
Borte took after her father and knew literacy. She was fond of the history of the steppe and neighboring China. Her father loved her and told her many stories.
Temujin stayed in the village of unigirats. Here one peculiarity of his was revealed — he was afraid of dogs. It speaks about his increased psycho-emotionalism, which is immediately felt by nomadic dogs getting used to a certain psychotype. Temujin was a passionary. Already in his childhood he broke out of the general row of calm and good-natured steppe people.
According to the «Hidden Tale» of the Mongols, on his way back Esugei was poisoned by the Tatars, having stopped at their nomadic camp as a guest. According to steppe tradition, it is a sin to poison a guest. The Tatars were not a completely nomadic tribe. It was a composite people, who roamed near the Chinese borders and due to long communication with the Chinese had a more plastic consciousness than other nomads.
Treasure Tale of the Mongols or Secret History of the Mongols or Yuan bi-shi or Yuan-chao bi-shi is the first of the known historical and literary monuments of the Mongols. Written in the XIII century, probably in Mongolian Uigur script, the author is unknown. It has survived under the Chinese name Yuan-chao bi-shi in the form of a text transcribed in Chinese characters — Wikipedia
There may have been no poisoning. Esugei was apparently ill and feeling his imminent death wanted to protect the first-born heir from the machinations of the Taijiuts. There is also a great probability that it was the Taijiuts who poisoned Yesugei. And the guilt was blamed on the Tatars, at whom Esugei stayed.
Before his death Esugei allegedly sent for Temujin his nuker Munlik. Most likely, either Oelun or Taijiuts, who bribed Munlik, sent for Temujin. Whatever it was, Temujin did not have time and arrived after his father’s death.
After the death of Yesugei, his family was no longer considered as extractors. Yesugei’s nukes went to other Mongol chiefs. Here there was a difference of ancient Mongols from other nomadic peoples. At that time Mongols were led by the Horde — a community of different tribal nomads, united by the conditions of life. At that time, for example, Turkic tribes lived in clan fraternities, which gave the possibility of transferring material values by inheritance and preserving the status at the death of someone.
As a consequence, the family of Yesugei was on the lowest level in the Mongolian hierarchy. They had no adult males who could be extractors. They had to be spongers in the Horde. The Taijiuts became the main ones in the Horde and their leader Targutai-Kiriltukh aspires to khan’s power. Of course he dreams of getting rid of the family of the claimant.