The Takumi-kun series showcases a LOT about origin Japanese yaoi and why it’s troubling, why it’s addictive, and what a core foundation it gave to the modern BL shows coming out of Thailand, Taiwan, and Korea particularly.

Beautiful fragile traumatized Takumi escapes the horrors of his youth by attending boarding school. There things aren’t great because his coping mechanism is touch-aversion, timidity, and fear. Alone and bullied, Takumi is barely surviving until handsome, rich, popular Gii becomes obsessed with him. Oh and they’re roommates.

The Takumi-kun franchise (like 2 Moons/2 Moons 2) shot this first movie and then recast for the remaining adaptations. The second cast is much better. They did not, however, re-film book 1 with the new actors, except as flashbacks. I highly recommend you watch the fan made first movie version (from those flashbacks) instead of this one, and then 3 of the 4 follow ups. So here’s a watching order:

Takumi-kun Series 1 DaiMao Version (Fan Made recut via flashbacks)
Takumi-kun Series 2: Rainbow Colored Glass
Takumi-kun Series 3: The Beauty of Detail
Takumi-kun Series 5: That Sunny Blue Sky

Series 4 is about side characters and doesn’t add to the main story, but it’s fine if you like those side characters.

This original Series 1 with the different cast is okay (I guess?) and a more honest adaptation of the original yaoi (which is NOT good), but not worth watching if you're looking to get into the series.

However, from a heritage BL film perspective this first movie (but also bits of the others) showcases how Japanese framing, filming angles, body positioning (staging), and cinematography for BL using the origin manga as a storyboard. This filming style would go on to influence Korean BL in particular (see Color Rush) and is still used in Japanese BL today (see Love Stage!!).

All that said, if you want a pitch perfect Japanese yaoi manga adaptation with none of Takumi's issues, Seven Days is your jam. Watch that instead.