First off, Ike and Soren cannot get an ending with anyone but themselves. Micaiah can support Sothe for an ending, as can Elincia and Geoffrey, and Lucia and Bastian, and Leanne and Naesala, and Boyd and Mist, but Ike and Soren can only have an ending with each other. Now, I think we can all agree that Micaiah and Sothe is their only “true” pairing, same with all the rest. Even Soren’s normal ending says he never used his talents for anyone but Ike. (Citation:
http://serenesforest.net/fe10/ending.html Soren’s endings)
Next, they have a special convo with each other. In it, Soren tells Ike that Ike is the only person Soren could ever trust, and Ike holds Soren. Now, the stereotypical man, since we all know stereotypes are commonly used in games, books, and movies, is unemotional. For Ike and Soren to show emotion is a rare thing among guys in Fire Emblem. Yeah, Eliwood cries for his dad, and Hector gets mad when he fights, but there are many other guys in that same game who show no emotion. Heck, most bosses are guys and they are just fighters, who make a stupid comment when they die. Then we have the stereotypical gay, portrayed as somewhat feminine, always being emotional. Ike and Soren show their true colors as the later category. (Citation: The transcript for this is found at almost every major Fire Emblem forum- I didn’t actually find one to be warned for advertising to link to. )
Third is the Path of Radiance Supports. Ike supports, as far as females go, Titania, Elincia, and Lethe. In the A support with Titania, he thanks her for all the help she gave his father, and even asks if she loved Greil. Obviously no relationship other than the almost mother/son one that was already there. In Lethe’s support, he is invited to come to Gallia. Lethe seems to respect him because of his strength, and, tempted with becoming a lot stronger, he agrees to come. In his support with Elincia, Ike promises to help her achieve her dream, his one support that may have implied at a special ending. However, Elincia already has one with Geoffrey, and Ike has one with Soren. Notice how all of the special endings in FE10 had a support in FE9, unless one of the characters was not there? Now, Ike’s support with Soren has him sharing his deepest secret, still wanting to have the friendship of the only person he trusts. Soren gets so emotional; they get a special base scene in FE10 that reveals some more of the situation. And Soren only supports Stefan other than Ike, who just has some branded information. (Citation:
http://www.feplanet.net/index.php?fep=main Path of Radiance Supports)
Fourth, Ike is very open. He’s not racist against laguz at all, being “different” himself. Soren is very closed off, but he is to everyone but Ike. Two different ways of dealing with a problem they both share. In addition, Heather obviously likes girls. That’s not in question at all, unless you think she wants to meet the queen for make-up tips of something. If there’s a girl who likes girls, why can’t there be a guy who likes guys? We’ve already had Erika x Ephraim and Raven x Priscilla, so a mature theme in Fire Emblem isn’t that revolutionary. Heck, even Dumbledore is gay. (Citation: J. K. Rowling interview, supports for FE7 + 8, FE9 + 10)
Fifth, and last for me at the moment, is that neither shows any interest in women at all. In FE9, Ike is credited with always taking his hand away when Aimee touches it. In FE10 he is only willing to flirt with her if she gives him a discount. Soren comes in, and let’s admit it, his compliments are so stiff and he maintains a straight face the whole time. He even denounces his comments by saying that what he does, he does for the good of the company. (Citation: Game Scripts at Gamefaqs.com )