During the time before Kaguya's 8th birthday, Tyler spent almost all his time with her, helping her train and improve her strength.
Thanks to the manual Tyler had given her, as well as his personal help, she managed to awaken the tenseigan and reach the Soul Refining stage of the Mortal cultivation realm. Unfortunately it seemed unlikely for her to awaken the rinnegan since she wasn't born with eyes in the palms of her hands… still, the tenseigan and her Soul Refining cultivation made sure no one under the Soul Ascension stage could harm her.
When Tyler wasn't training Kaguya, he created a new clone technique loosely based on the shadow clone technique that might come to exist in the future, he called it reincarnation clone, since it primarily used reincarnation laws to work. The clones that he created would be no different than himself, they were connected with him at all times, but could also think independently if required. If he were to describe it in terms from his first life, he was a player, and he had multiple avatars he could choose to control.
It was like playing a two player game by yourself, controlling both characters and looking at two screens at once. He could choose the focus his complete attention on one at a time if he so wished and if one of them or his "main body" got destroyed, it wouldn't matter, since he could just use one of the other bodies.
Unfortunately, controlling more than two avatars at the same time was quite hard. His current limit was 4, 5 if he pushed himself, but since the clones could also operate independently, he could create as many as required and they could send back their memories periodically to keep him updated in a similar fashion to shadow clones.
It was somewhat similar to creatures with a collective consciousness only that he had one main consciousness controlling multiple bodies that could send him information. It was hard to describe.
Naturally he sent his avatars out into the universe in order to get a better understanding of this world. After all, there were many things that were never shown in the Naruto anime or manga… there might be some incredibly bullshit and OP things out there, though he doubted they were stronger than himself, it was better to be paranoid than to have unknown threats come to bite you in the ass.
Luckily the Otsutsuki clan was well protected and hidden from most threats since it resided in a sort of personal dimension that only clan members with 1/4th blood purity or higher could access.
He would have used the fidelius charm from his days as a wizard to make it even more secure, a dwelling whose location has been protected by this spell is invisible, intangible, unplottable and soundproof after all, but it was truly unfortunate that this universe didn't seem to contain any ambient magical energy, nor was he born with a magic core that wizards primarily used, making it impossible for him to cast any spells.
The time flew by rather quickly, and Kaguya finally turned 8 years old. Her birthday party also signified a sort of farewell, so the whole clan participated and wished them luck on their journey.
Tyler: "Farewell everyone! We'll come and visit whenever we can!"
Kana: "You two be careful out there you hear?!"
Tyler : "Don't worry mom, see you soon!"
Kaguya and Tyler both said their goodbyes before Tyler tore open a portal to exit the clan dimension.