The image looks nice. And most Japanese will probably understand the meaning (if explained).
But, it might be at first glance viewed as Chinese rather than Japanese. I think it would be acceptable if a Chinese speaker thinks it looks OK.
Speaking from the Japanese perspective, 恒 I think is permanence in the way that something is always there, such as 恒星 (a star in fixed position) and 恒久平和 (everlasting peace).
Just for your information, I thought up a couple of words for "eternal":
不滅 (fumetsu) / 無窮 (mukyu) / 千年(sennen, meaning millenium but can suggest a sense of eternity)
This is about what I could think of... Others may have better ideas...