The psionics system is not being used in Eidolons. However, either a runemage (i.e., wizard) or geomancer (i.e., sorcerer) could thematically function as a psion, for the purposes of this campaign. As a runemage, just take spells that reflect the types of abilities you want your character to have. If there is a psionic power for which there is no comparable spell, we can probably approve it on a case-by-case basis. Runemages are covered in tattoos, and must concentrate to focus the runes in their mind, so it is a very psionic process thematically. Or as a geomancer, you would work with us to come up with thematically appropriate abilities relating to the flow.