Although being friends with Takayuki, Haruka and Mitsuki in high school, he drifts off from the group after graduation. However, he becomes an important character towards the end of the series. He sometimes presents a counter-balance to the drama of the rest of the characters, as his relationship with his girlfriend (who remains off-screen) seems to be going well.  (Source: Wikipedia)

At first, Takayuki Narumi is befriended by Mitsuki Hayase only because Mitsuki's best friend, Haruka Suzumiya has a crush on him; however since then, Takayuki, his pal Shinji Taira, and Mitsuki have grown to be the best of friends. Then one day, Haruka confesses to Takayuki her love for him. Not wanting to hurt her feelings, Takayuki agrees to go out with her. After a few incidents, their relationship gets intimate, even while Takayuki and Mitsuki begin to realize their feelings for each other. But suddenly, when tragedy strikes, things are never the same for these four friends again.

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After Haruka Suzumiya got out from the hospital from her three years of coma. She moved back to with her parents and continued to date Takayuki Narumi. She wanted to see her old friend Mitsuki Hayase who Takayuki Narumi dated while she was in coma.
 
(Source: Anime News Network)

Novelization of the Rumbling Hearts (Kimi ga Nozomu Eien) anime adaptation.

In Muv-Luv Alternative, Takeru wakes up three years after the end of Muv-Luv Unlimited to find himself back in his room. Although he first thinks that everything that had happened to him was a dream, he soon feels that something is wrong, and leaves the house to find that he has been sent back in time to the beginning of the events in Unlimited. Unwilling to accept something like Alternative V, he decides to help professor Kouzuki to complete Alternative IV and save mankind. 
(Source: Wikipedia)

At first, Takayuki Narumi is befriended by Mitsuki Hayase only because Mitsuki's best friend, Haruka Suzumiya has a crush on him; however since then, Takayuki, his pal Shinji Taira, and Mitsuki have grown to be the best of friends. Then one day, Haruka confesses to Takayuki her love for him. Not wanting to hurt her feelings, Takayuki agrees to go out with her. After a few incidents, their relationship gets intimate, even while Takayuki and Mitsuki begin to realize their feelings for each other. But suddenly, when tragedy strikes, things are never the same for these four friends again.

The MagiQ anthology manga of the popular visual novel "Kimi ga Nozomu Eien" by multiple authors.