Its said that Ennin received 13 empowerments, including a few not received by Kukai, which shaped his understanding of Taimitsu in the Tendai context.
One thing to keep in mind is that in the early days of Tendai things were not so doctrinally coherent and shaped. The narrative about Ennin specifically going to get empowerments and knowledge to make up for what his master was lacking is maybe a product of later times.
Let me point you in the direction of a PhD dissertation that you might appreciate:Searching for the law: Ennin's journal as a key to the Heian appropriation of Tang culture http://gradworks.umi.com/33/80/3380358.html
From what I've gathered from other readings, this mainly has to do with his reception of the SuSiddhi which Kukai did not receive.
I don't know for certain, but the emphasis on the Su-siddhi empowerment again might have been a later development in the lineage narrative.
Ennin's original intention was to go to Tiantai, but ended up at Mt. Wutai and then Chang'an. If he had been able to visit Tiantai, he might not have received so many empowerments including the Su-siddhi.
Let me quote the above paper:
Esoteric Instruction and Ordinations
Although the search for esoteric Buddhist credentials and materials were
ostensibly Ennin’s primary purpose for traveling to China, they take up surprisingly little
space in his journal. Ennin kept many notes about his copying and acquisition of texts,
but these say nothing of his perspective on these texts and on esoteric ritual. Likewise,
when Ennin notes in his journal the esoteric instruction and ordination he received these
notes are brief and sometimes cryptic. Overall, the time Ennin spent in Changan studying
esoteric Buddhism and receiving initiations is among the least well documented in the
entire journal. There are several possible explanations for this paradox. The most likely
is that the information was recorded in other places, such as the sutras and commentary
he was copying and so he saw no need to be redundant. Perhaps the journal functioned as
a place for information that was important but not recorded elsewhere.
Although Ennin was very motivated to study, receive initiations, and bring back
texts and ritual implements—enough to attempt to abandon the ship under uncertain
circumstances—there is nothing in the journal that indicates that he views esoteric
Buddhism as fundamentally different from any other form of ritual practice. In fact, as
far as we can tell from the journal, he pays much closer attention to various non-esoteric
rituals. It is only after he has received esoteric instruction in Changan, escaped the
Huichang persecution, and returned to Japan, in short, after his journal is written, that he
begins to formulate his own theory of how esoteric ritual fits into the more fundamental
Tendai doctrinal scheme.
In fact, the consensus view is that this process is fully
completed only by Ennin’s disciple, Annen ( 843-915?).26 Thus in most of the
journal, although Ennin is collecting esoteric texts, his view of Buddhism and of ritual is
unaffected by the esoteric Buddhist worldview.
The traditional account is that Ennin traveled to China to remedy Saicho's lack
of esoteric knowledge and credentials and thus fully esotericize the Tendai sect.27
Although esoteric ritual eventually became a central component of the Tendai sect’s
identity, we should not necessarily view the entire process as teleologically
predetermined, inevitably leading to this point. Later Tendai monks have that tendency
when they depict Ennin’s somewhat random wanderings as a carefully planned itinerary
centered on the study of esoteric Buddhism.28 They also project later doctrinal
formulations back onto this earlier, less doctrinally coherent time. The journal provides
the main antidote to these readings, since it provides little support for them and much
On the one hand, it is clear that Ennin is seeking after esoteric Buddhism, both
from the anecdotes explaining why Ennin wanted to go to the Tang, and his own dreams
recorded in his journal.29 On the other hand, Ennin seems primarily motivated by a
desire to finish his master’s incomplete business, rather than an intrinsic interest in
esoteric Buddhism, since Ennin was not a student of esoteric Buddhism prior to traveling
to the Tang.
Ironically, had Ennin’s travels proceeded according to his initial plans, he may
never have received the esoteric training and initiations that he did in Changan. His
original plan was to travel to Mt. Tientai and on to Changan, as time permitted, and then
return with the embassy. Had he been able to travel to Mt. Tientai, he may have felt his
mission complete and returned with the embassy to Japan, without ever traveling to
Changan or Mt. Wutai.
How did this extra learning if you will, effect the understanding of mikkyo in the Tendai context that differs from the Shingon one?
Let me see if I can find a paper that deals with this.
Do you read Japanese?
Incidentally, I also wrote a brief article on Ennin which might be of interest (mostly about his journal which I enjoy reading and studying):https://sites.google.com/site/dharmadep ... nd-journey