yea! i agree with you on that. he is just a perfectly extreme yandere seme. i think he initially was jealous of him & wanted to torment him but that gradually turned into possessiveness. from a creepy aspect, i think the author did a great job with the character & plotline. there could've been a better build up if this had more volumes though.
Hmmmmmmmmmmmm, idk about "perfectly extreme gender seme" there are a lot of those-
True Yoshiki is very possessive, and most definitely psychotic- we see tht in the last panel (though he might actually be sociopathic idk)
BUTT- and it be a biggish butt- he was originally jealous of Tsukasa (es mi casa) most yandere characters are crazy 5 mins within meeting the mc. Yoshiki wasnt like tht.
Here's the Spanish translation: https://qvfammaonline.blogspot.com/2019/03/imitation-mate-capitulo-04.html?m=1

I THINK THAT YOSHIKI LOVE TSUKASA HONESTLY, BUT BECAUSE HIS POSSESSIVENESS IS TOO HIGH, WHICH IS THE REASON FOR HIS CREEPY SMILE AT THE END.
AND IN THE EXTRA, HE TRIED TO IMPREGNANT TSUKASA SO THAT TSUKASA WILL BE FOREVER BIND TO HIM?!?!
That's my idea, anyone with me? (/TДT)/