Dictionary / Vocabulary / 馳せる
はせる
to run; to hurry (when going somewhere); to drive (a car) quickly; to ride fast (on a horse)
いつもお世話になっていますから、一旦緩急あれば、すぐさま馳せ参じます。
You're always there for me, so if you're ever in dire straits, just let me know and I'll come running.