- Why has Kail not, at the very least, attempted to tell anyone that he's from another timeline? I could understand that many people would find it hard to believe, especially since at the point of the story he is sent back, Kail is just a nobody that has no name or title to impress anyone with, but at the very least, he could have attempted to tell his mother, Selaia, who even had a long chat with Kail about how it might be possible to time-travel if certain items are collected. You'd think that since he's already witnessed what was practically the end-of-the-world, he would try to inform folk of what is going to happen with the Demon Lord's Great Invasion, but he hasn't attempted it once apart from having his memories read by Sildonia Zeeles.
- He didn't intend for Sildonia to read his memories: it's just one of the things that happens when she imprints on her master. The official answer to your question appears to be two fold. First is that he worries people won't believe him and/or think he's insane. Even his closest friends aren't exceptions from this, because he can't afford to have them question his motivations or believe stress is getting to him. The second reason is he doesn't want those who would believe him, to be too reliant on his recount of how events occur. This especially gets reinforced as he slowly becomes aware that his actions are changing the timeline enough, to make his own recount inaccurate. A third matter worth considering: there are some individuals who might react badly to info in the other timeline. Riize knowing Urza became his wife could be a touchy subject; another would be Minagi discovering he's responsible for ruining her initial start to become the world's greatest assassin (or that in the original timeline, some of her actions actually CAUSED the demons to gain such significant victories). Ultimately it comes down to Kail believing — and not without justification — it could do as much harm as it would good, in revealing the truth. It's a slippery slope that just gets more slippery.
Headscratchers / Tsuyokute New Saga