Ayumi, a cheerful, Book Dumb, Genki Girl who's an ace in track and field but secretly has a lack of self confidence in herself to the point she faked an injury before the finals because some jealous seniors looked down on her. Keima, in a moment of kindness, consoles Ayumi that she should believe in herself as he believes in her which comforts her and leads to their first kiss. Aww....
Mio, a short, snooty rich Tsundere who acts high and mighty, who is secretly hiding the fact she's not rich anymore. However, she's pretending to be rich not because she's stubborn, she's doing it because she can't accept her father's death. But Keima manages to convince Mio that this isn't what her father wanted for her - what her father really wanted is for her to be happy. These words and the fact Keima cares about her helps Mio let go of the past, move on and be happy for herself.
Kanon, a popular idol with some Yandere issues over people not noticing her. She wants attention not because she's an attention seeker, she wants it as proof that she is no longer the nerd that everyone forgets. Without that attention, she feels like she has failed and becomes invisible literally. Keima, on the other hand, doesn't believe so, as the fact she worked hard to become an idol and her fans love her is the proof that she has truly come out of her old image. Thankful, she kisses him for helping her realize the truth she didn't notice all along.
Shiori, a shy bibliophile who doesn't talk very much and loves books to the point she locks up the library in protest to protect the books from getting dumped for a media room. Keima exposes the truth as Shiori not acting to protect the books, but herself, as she wants to talk to people but is too shy and afraid of being misunderstood. With the truth in her face, she almost breaks down but Keima picks her up and tells her not to be afraid since he'll be there to help her. His encouragement and kiss finally helps Shiori gets over her shyness.
Kusunoki, a tomboy and Captain of the Girls' Karate Club who rejects femininity in order to inherit her family's dojo. Yet in reality, she wants to be girly despite her seeming hatred of it. This causes her inner conflict to the point her feminine side splits from her. After she and her feminine side fight to be the dominant personality, Keima convinces them that instead of choosing either being masculine and feminine, she can be both. This finally convinces Kusunoki that there's nothing wrong with being girly - including falling in love with Keima.
This one is especially heartwarming. Kusunoki started out believing that Keima was a waste of time, but she soon came to respect him enough to talk to him, as an equal, about her problems and listen to Elsie's ridiculous proposed solution on his say so. Until this episode, only Elsie and the gaming community respected Keima that much.
Haqua, Elsie's demon best friend and genius in the Weiss hunter squads, who Elsie believes is the greatest demon. In reality she isn't; she has yet to catch a single spirit and is ashamed to admit the truth to Elsie, to the point a Weiss possesses her. When Elsie learns the truth from a possessed and ashamed Haqua, Elsie just hugs her - it doesn't matter, because in her eyes, Haqua will always be the best demon she has ever known. Not only does it lift the pressure off of Haqua but it frees her from the Weiss' control.
Then Keima, realizing he's been a jerk to Elsie, actually compliments her. Elsie is so overjoyed! Just the look on her face right then! She acknowledges she does have her faults and accepts his apology in one swift promise, offering him a meal on her - something bought, not something she made.
Chihiro, an average girl with no interesting traits who secretly wishes to be special to the point she confesses to any guy she fancies. When she realizes she's in love with Keima after he helps with her latest crush, she tries to call it off, which angers Keima. Big mistake, since this only convinces Chihiro that she will never be special. Fortunately, after realizing his mistake, Keima confronts her, gives her a "Shut Up" Kiss and tells her as long as she truly wants it, nothing can stop her from becoming special.
Jun, a bright, idealistic teacher who truly wants to help her students to reach their dreams, something she failed to do with her teammates during their high school basketball team, because they felt she was trying too hard. When history repeats itself with the class, she feels dejected, feeling all the work she'd done to help them was for nothing, but Keima comforts her, telling her it wasn't because she was trying too hard that she failed, she failed because she didn't try enough. That, and the class coming to apologize, bring her relief that she did succeed.
Tsukiyo, a loner who'd rather watch the stars with her doll in her own world rather than get involved in real life, because she's seen its ugly side after her parents' divorce. After she shrinks to the size of a doll, Keima tries to dissuade her from living like her doll, and finally convinces her that despite how ugly life is, there is still beauty within the real world.
Minami, a middle schooler who is undecided if she should continue swimming lessons as she's afraid of change. Falling in love with Keima, he convinces her that moving on and accepting the past is a part of growing up and kisses her.
Tenri, a shy girl who fell in love with Keima as a child but is afraid to admit it. After a series of misunderstandings, and getting chased by Nora, she finally gets to kiss the boy she loves.
Rieko, a grandmother who longs for the past. Her Weiss grants her wish by allowing her to project a younger spirit which haunts her village cemetery. After Keima figures it's her and talks with her, Rieko admits while she is sad that her old friends and family are no longer with her, she is still happy with the life that she lived.
Sumire is the daughter of a ramen chef who owns a failing Chinese restaurant and wants to help him by creating new ramen for the restaurant. But her father refuses to accept her help, because unknown to her, he wants her to have a better life than being a ramen chef. After Keima manages to get Sumire and her father to talk to each other, Sumire's father realizes his mistake and finally acknowledges the path his daughter wants to take. In thanks for helping her, Sumire promises to cook Keima any ramen he wants and kisses him.
Nanaka, a classmate of Tenri's who's so obsessed with her pride in being an champion shogi player that she won't stop challenging Tenri in shogi until she wins. After a training regime with Keima, Nanaka realizes that winning isn't everything and stops being prideful.
Yui, a rich girl who is controlled by her mother to live a life that doesn't allow her any freedom to choose. After switching bodies with Keima and almost enjoying her new life, she realizes she loves Keima, for it was he who helped her gain the confidence to face her mother and be independent.
Hinoki, Kusunoki's older sister who acts like a Crazy AwesomeCool Big Sis to everyone including Kusunoki. In reality, her image is a lie to please Kusunoki and is causing a considerable amount of stress. Fiore tricks Hinoki into believing Kusunoki hates her, enabling a Weiss to possess her, and causing her to become a giant. Kusunoki confronts Hinoki, who the latter admits hated Kusunoki for making her pretend to be the Cool Big Sis rather than have the life she wanted. Even after this and a fight, Kusunoki hugs her sister and tells her that she is sorry for what she went through - but she never wanted a Cool Big Sis, all she ever wanted was the sister she loved, which frees Hinoki of the Weiss's control.
Akari, a dirty looking scientist who tries to create the perfect human being because humans are flawed. Yet it is Keima who manges to convince her that being imperfect isn't so bad.
Urara, a little girl who wants to be an adult. After her parents died, she was raised by her grandfather, who became consumed with the desire for revenge against the devils that killed his son and daughter-in-law. Seeing how lonely her grandfather was after her parents' deaths, Urara wanted to grow up quickly so that she could be there for him. When he realizes how distant he's been, and how much Urara loves him in spite of that, he opens up his heart to her and allows Urara to fill the gap in hers.
Haqua telling a sleeping Keima how she sort of really feels at the end of FLAG 144.
One moment was when he was talking with Akari and realizes that living in an imperfect world isn't so bad.
"If the world is perfect...then there wouldn't be a need for love now would there?"
Two other moments that also reflect on it were on the last act of the Nagase arc.
"...It's strange. When shenote Nagase feels down, for some reason...I care."
And following the above, when Nagase leaves the academy, she runs into Keima and apologizes for misunderstanding him. Before she finishes, Keima gives us the below line. It may seem small, but it says a lot about Keima.
This comes to a long-since-coming head when Tenri shows Ayumi the letter Keima gave her in FLAG 263, wherein Keima lists the good points of the Goddesses' Hosts and what he believes is what makes them special, then continues on by stating pure heartwarming:
In fact, the half of the chapter that isn't about Keima fulfilling his mission in the past is basically one giant Crowning Moment of Heartwarming for both Tenri and Keima; Keima for the above, and Tenri for demonstrating once more that she steadfastedly remains his devout and staunch supporter.
FLAG 103 as a whole. Elsie is depressed because she couldn't capture a runaway spirit, and Keima wants to cheer her up, even going to Chihiro and Ayumi for help. The two set Elsie and Keima up for a date, but it doesn't go as expected...So Keima does the sure-to-work thing: Taking Elsie to the Fire Station, the equivalent of an Amusement Park for her. Then in the end, Mari thanks Elsie for how much she helped change his life and asks her to continue to watch over Keima.
Ayumi's answer to Chihiroin FLAG 157 is one to anyone who remembers the reason she had a weiss inside.
Tenri using her magic tricks to cheer up Keima while he's depressed over breaking Chihiro's heart in FLAG 168 and saying she loves him just the way he is.
When Haqua escapes from Hell and meets up with Keima for the first time in a week, there is something distinctly heartwarming about how she just smiles and goes along with his zany plan instead of complaining like usual.
Haqua: Heh. You haven't changed at all.
Elsie, a demon, gets fully accepted into Keima's home as his sister. His mother even threatens a divorce because she believes Elsie is her husband's daughter from an affair, but she still welcomes Elsie into her home, and treats her like her daughter who's been living there for her whole life.
Becomes more poignant when we learn about Elsie's background as an orphan, and that she doesn't remember her birth parents - as far as she's concerned, the Katsuragis are her real family.
And finally, in the penultimate chapter, via Cosmic Retcon, Elsie becomes Eri Katsuragi, making them her real family for real.
Elsie: You said to do as I pleased, didn't you? I want to be with you forever! (Imitating Keima) I can see it!! (Turns back to Keima with a smile) This is my ending.
Flag 250: Dokuro stays behind to deceive Vintage for the next 10 years, and she and Keima agree that even if they should meet again, they must pretend not to know each other. However, she promises she will always be there to watch over him. Then she puts on a certain black collar...
FLAG 267-268. Keima confesses to Chihiro. She rejects him, but agrees to go on a date with him before the end of the day. Furthermore, the reason Keima insisted on choosing someone immediately was so that the other girls could move on rather than being stuck vying for his affections forever. His conversation with Nikaido also confirms that he didn't just pick one at random; he does love Chihiro.
Wakaki's own life story is pretty heartwarming too - after being given the Shogakukan Comics Award grand prize and being told his future for the next ten years were anticipated, multiple oneshots of his were shot down. He tried to work as an assistant, but it didn't get him anywhere, so he returned to his hometown of Osaka depressed. He then began to start a life as a hardcoreshut-in. Thirteen years after the prize, one of his oneshots, "Holy Crystal Albatross", got published, and got quickly cancelled because of "low popularity". His bank balance dipped to below 10,000 yen - if he didn't get any money soon, he'd fall into debt. Finally, he submitted The World God Only Knows and it became a smash hit online. Though it came close to being cancelled, it struggled through - and Wakaki managed to save his own life.