Like he thinks the seme is either scary( when he's not, he just seems that way) or his rival for some reason or other :3

Enemies Become Lovers Category:
Junketsu Drop
50 x 50
Kage Aru Tokoro ni
Kowarekake no Omocha ch6
Oresama no Toriko

Rivals Become Lovers Category:
Tsumasaki ni Kiss
Miteranneeyo
Koko kara Dousuru?
Koi o Suru DNA +
Dear My Mister

Rivalry Category:
Rival ni Ki wo Tsukero
Saa Koi ni Ochitamae
Aisaretaino

AND since I'm too lazy to list more, look this topic and this topic for more.

Edit: Oh, forgot you asked for "scary seme" too. I have just a few recommendations for this one:
Appearance Different from Personality Category:
Kawaii Beast ch1
The Miscreant Next Door
Sugar Code
Urahara to Dilemma, if I remember right...
Katsubou no Manazashi
Ore ni Koi Shite Dousunda
Ginyuushijin no Koi

Check this topic for more. I could try listing some more, but only if you are into the "delinquent" type too (I love delinquents! <3).