The second page of the letter reads

"In year 2013, Natalia and I have been together for 10 years.

On the anniversary, she wanted a gift, that is to use the time machine to time travel, to avoid a car accident that caused a scar on her face.

I predicted that will change the timeline from there onwards. In case you both only know each other by now, that means history for my timeline had changed.

Predicting that might happened, I wrote these two letters, signed up with a safekeeping services so that it will send the collection reminder to both of you, with two purposes:

1) to safeguard my invention: time machine
2) to inform you that Natalia is the greatest person to be with.

Apart from that, I can also get to confirm two theories (I guess you will be the one confirming that, if the timeline has changed):

1) Changing a past event can affect the timeline from that point of time onwards.

2) if that is the case, whoever makes the changes will disappear from the timeline, because that person is no longer relevant.

Sounds complicated? I'll write a chronology of the timeline that happened during my time, to let you understand better"