To be fair - as someone who wasn’t on Tumblr at the time but still found/finds Loki attractive (and is ace) - I feel need to add some stuff.
1 - Loki was actor Tom Hiddleston’s first major role. (Fun fact: He originally auditioned to be Thor)
2 - I don’t think Tom was originally thought to be conventionally attractive. When the character was first introduced but especially in The Avengers (2012) a lot of male fans and critics were surprised by how many female fans preferred him to the more stereotypically masculine actors.
I would say he is the template for all Tumblr Sexymen
The Tumblr sexyman can be anyone - animated or real - but cannot be someone who fits into the idea of what cis, straight men THINK women consider attractive.
Thor - for example - would be considered sexy by patriarchal standards but isn’t a Tumblr Sexyman.
The villain from the Osmosis Jones movie? Clearly made to be sexual, isn’t conventionally attractive. Is a Tumblr Sexyman. Same with the pollution monster from Ferngully.
Does that make sense? Now for the finalists
I wouldn’t classify Ryland Grace as Sexyman ™ . I can absolutely see the appeal - but Ryan Reynolds has always been considered sexually attractive by the patriarchy.
Senshi, in the English dub, has the benefit of being voiced by SungWon Cho - whose voice many people find attractive and is probably the main appeal.
Tenna …just fits the aesthetic. I don’t know anything about the character but yes, that’s a SexymanTM on sight.