Right off the bat, What could be described of the room from where the almost deathly voice came was, dark.  Read this sentence out loud, it's painful, this could be in an active voice instead, to give more power to the type of narrative. HunterxHunter is a great example of something to learn with.

With a powerful tool such as the narrator, especially in the way the author decided to go about this novel, it is to be expected to avoid the MC speak things like the second part of this sentence.
"Err... right. I guess I'll just go off what little information I can remember. My memory has deteriorated over time, so I'll try to be as specific as I can." The later half is an example of what the narrator must say.

See you tomorrow." Michael bid goodbye to Lopez, who had already entered the elevator. -> See you tomorrow, " Michael bid goodbye to Lopez, who had already entered the elevator.

If same person as the one doing the action you do, " if not."

Chapter 2: The beginning of chapter 2 

Krodoa was such a heavy info dump that most readers would tell you, "show don't tell." You could've made a little scene as a baby and connect the dots through a book, or the MC sneaking on a lesson to the older sister as he crawled or something. You'd earn a lot more points that way in grabbing the reader's attention.

 And besides, I might be able to learn a thing or too from you."

Chapter 3:

"Good morning, Mother." Upon reaching the kitchen, Kenneth greeted his mother, who was preparing breakfast. "Good morning, you two. Just a minute, I'm almost done with cooking. Lena, dear, could you help me prepare the plates?" Mikaela called Lena, who was playing with Kenneth's hand. (You have this tendency to repeat through narration what the characters say.) Also, "you two" needs a, <upon her son words, she looked at them with a kind smile, having both her hands busy with preparing breakfast. Thus, she glanced at Lena who seemed free, watching her playing with her brother's hand. "Good morning you two. Lena, dear, could you help me prepare the plates?"

"Right away, Mom. Oh, we're having bacon and eggs, my favorite!"