Kasumi Takano's Links
Kagome and Kasumi are childhood friends, and went to the same elementary and middle schools, though Kagome is Kasumi's junior by two years. They lived fairly close, and Kasumi's dad took Kasumi and Kasumi's mother to the Amamiya family shrine to pay respects to the gods every so often. As a result, Kagome and Kasumi started to become friends despite the slight age difference.
Kagome admires Kasumi, and sees her a bit like an older sister. She was a bit sad to see Kasumi going to Shiketsu, since Kagome had planned on going to UA, but is happy for her regardless. They still text and stay in touch
Ryu and Kasumi are childhood friends, quite literally kids next door. They always got along well. In kindergarten Ryuu and Kasumi had their first sweet innocent smooch, and from then on Ryuu was a goner. He kept proposing to her with various items - all of which she kept in a box, and she kept referring to herself as his wife.
When they got into their early teens, he asked her all officially to be his girlfriend, and she just gave him a dumb look and asked "I thought I already was?" and to which he just grinned widely and said "Damn right you are!".
They've been dating steady ever since, without any issues. They are on the same page regarding where they want their relationship going, and what they want in the future.
At Shiketsu, due to school rules, they could never explicitly say they were dating, but most people figured it out regardless. Especially with how seamlessly they work together, being able to intuit what the others wants to do and means to do on the field in a split second. Their quirks are incredibly compatible, but as are their personalities
Camie was an exception to this, and tried to flirt with Ryuu - to which Kasumi just had a good laugh at Ryuu's discomfort. She is secure in his feelings for her, knowing he'd never look at another woman like that.
During the graduation ceremony, the moment after they were graduated, Ryuu went down on one knee and proposed properly to her in front of the whole school. He had a whole speech planned, but was choked up and unable to say it. All that mattered in the moment was her, and her "yes".
Knowing that hero life can be incredibly unpredictable, he did not want to waste any moment marrying her, thinking that every moment counted. He wanted her to be his wife for real and not just them playfully calling her that