Consider Tamao’s poem in the "Etoile" episode. She expresses a love for the rainbow, even though it is an ‘illusion," to express–as the president of the Poetry club explains–the painful feeling of unrequited love. We see here a foretelling of her own romantic fate perhaps, and also an admission of her incapacity to see the beloved except as an illusion distanced from her, reconciled only within poetry, the conventional expression of language.
Nagisa is unable to create poetry; she admires Tamao for her ability. Yet she has a strong capacity to perceive and to respond to beauty. At various points she is stopped short by the overwhelming beauty of what she sees: once when she comes out upon the edge of the lake, and once in the library, when she is struck by the beauty of the light coming though the colored glass. And of course her first thought when she first sees Shizuma is to think how "incredibly beautiful" she is. If there is a distinction between Tamao and Nagisa here, it is between mediated and immediate experience.
This immediacy of experience will be a point of connection between Nagisa and Shizuma. When we overhear Shizuma’s inner musings, of desolation and alienation from nature, we recognize at once that her life _is_ the poetry that Tamao merely circumscribes. Shizuma has already lived a life of romance, of love and loss, which Tamao can only imagine.
So it turns out that Shizuma and Tamao’s responses to Nagisa are subtly different. If both are drawn to her appearance, to the cuteness all agree she epitomizes, for Shizuma she is, as she tells Miyuki, a flower she cannot help but touch, an experience within her already adult romantic life. For Tamao, she is an object, recorded in her details in Tamao’s little book, almost a "plaything," as Nagisa complains, a sign of Tamao’s relative immaturity.
Nagisa will prefer to be a flower to a rainbow, will prefer actual experience to imaginary life. It is not even a matter of preference: that is how she is. The development of her character in the anime follows this lead: she is cheerful, direct, active, a person who loves eating, new clothes, friends, etc. She enjoys and embodies uncomplicated life.
Certainly Nagisa is swept away by Shizuma. But we can also recognize that her vitality seeks its correspondent in Shizuma’s wildness of soul. Like Hikari and Amane, Nagisa and Shizuma are spiritual counterparts.