The story follows , a young soccer prodigy raised by his older sister, Reiko , following their parents' death.

Regarding the quality and availability of "better" subs for episodes 1, 2, and 3:

Now, to the crux of your keyword search. You specifically looked for "shounen ga otona ni natta natsu cap 1 2 3 sub better." You are not alone. Here is the technical and artistic breakdown of why the Original Japanese Audio with Subtitles (Sub) vastly outperforms the English Dub for these specific three chapters.

Here is a breakdown of the opening trio of episodes, and why watching it elevates the material from a standard teen drama to a deeply moving character study.