Board Thread:Questions and Answers/@comment-26335544-20150423134142/@comment-5161123-20150428053318

Selena is the strongest 7* hero because of her sustain and extra skill.

Lexida heals per turn and due to its double-hit buff, Selena generates lots of BC, which can be used for her SBB, which pretty much doubles the amount she heals per turn for three turns. And with her extremely high REC, she'll both deal and receive heals harder.

Her Extra Skill gives a 20% boost to all parameters which really helps, and it also gives an Angel Idol Buff that activates at 20%. Unfortunately, that means units like Rowgen can still one-shot because they deal so much DPS. Note that you need Lexida for all the perks.

Also worth noting is that she has great cleavage in her 7*.